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Baking dish filled with green bean casserole.

Healthy Green Bean Casserole

This Healthy Green Bean Casserole is a lighter alternative to the traditional green bean casserole but without any canned goods or fried french onions! It is made entirely from scratch with fresh green beans and mushrooms in a creamy sauce with an extra crispy onion topping!
Course Side, Side Dish
Cuisine American
Keyword Casserole, Green Bean Casserole, Healthy Green Bean Casserole, Thanksgiving
Prep Time 20 minutes
Cook Time 1 hour
Servings 8 servings
Calories 235kcal
Author Samantha Buckner


For the crispy onion topping:

  • 2 medium yellow onions, thinly sliced
  • 2 tablespoons olive oil
  • 1 cup panko breadcrumbs
  • 1/3 cup freshly grated parmesan cheese, fresh is best!
  • 1/2 teaspoon salt, more or less, to taste
  • 1/4 teaspoon black pepper, more or less, to taste
  • 1/2 teaspoon garlic powder

For the green beans:

  • 2 pounds fresh green beans, trimmed and cut into bite-sized pieces

For the mushrooms:

  • 1 pound baby bella mushrooms, washed and sliced thin
  • 2 tablespoons unsalted butter
  • 1 teaspoon fresh thyme, or 1/3 teaspoon of dried
  • salt and pepper, to taste

For the sauce:

  • 2 tablespoons unsalted butter
  • 1/3 cup all-purpose flour, or GF all-purpose flour
  • 2 cups unsalted vegetable stock, or chicken stock/broth
  • 1 cup milk, dairy or dairy-free
  • 1/3 cup freshly grated parmesan cheese
  • 1/2 teaspoon garlic powder
  • 1/2 teaspoon salt, more or less, to taste
  • 1/4 teaspoon black pepper, more or less, to taste


Crispy onion topping:

  • Preheat oven to 425 degrees F.
  • Line a baking sheet with parchment paper and set aside.
  • To a large mixing bowl, toss the onions with the olive oil to fully coat.
  • To a medium mixing bowl, combine the breadcrumbs, parmesan cheese, salt, pepper, and garlic powder.
  • Add the breadcrumb mixture to the onions and gently fold everything together. Spread out into an even layer onto the prepared baking sheet.
  • Bake for 15 minutes, stirring or flipping halfway through.
    Remove from oven, set aside, and lower the temperature to 350 degrees F.

Green beans:

  • While the onions are cooking, bring a large pot of salted water to a boil. Add the green beans, cooking 3 minutes. Drain and rinse in very cold water to remove any heat to stop the cooking process. Drain well and pat dry with paper towels if needed.


  • Meanwhile, place a large saucepan over high heat with 2 tablespoons of butter. Once the butter is melted and bubbling, add the sliced mushrooms. Saute for 5-7 minutes or until all of the moisture has cooked out and they are golden brown. Season with salt, pepper, and fresh thyme.
  • Remove to a bowl or even the pot you used to boil the beans (one less dish to wash) and set aside.


  • Place the same saucepan over medium heat. Add 2 tablespoons of butter and once melted and starting to bubble, sprinkle in the flour, whisking until a paste forms.
  • Slowly poor in the stock, whisking consistenly and vigorously until no clumps remain. Pour in the milk and raise the temperature to medium-high heat to bring to a boil for 1 minute before reducing to a simmer for 3-5 minutes, stirring often until the sauce begins to thicken.
    You want a thin, gravy-like consistency.
  • Turn off heat, add the parmesan cheese, salt, pepper, and garlic powder. Stir until the cheese has melted.

Putting it together:

  • Spray an 8x12 or 9x13 baking dish with nonstick cooking spray. Add the green beans and mushrooms.
  • Pour the sauce overtop and stir to coat.
  • Top with the onions, cover with aluminum foil and bake for 15-20 minutes. Remove foil and bake for an additional 5-10 minutes, keeping an eye on the onion topping.
  • Garnish with freshly cracked black pepper, additional parmesan cheese, and freshly chopped thyme. Serve hot.


To make gluten free:  use gluten-free breadcrumbs and gluten-free all-purpose flour.
Vegetable stock: can swap for vegetable broth, chicken broth, or chicken stock.
Sodium:  If using regular broth or stock (rather than unsalted), I recommend seasoning with salt, to taste.
Milk: We use cashew milk, but you can use heavy cream, half and half, regular milk, or another dairy-free alternative (although I cannot attest to the results with all dairy-free options).
Extra-crunchy onion topping: If the onions are not as crispy as you would like them to be, simply turn the oven to low broil and allow the topping to cook for 2-3 minutes. Keep an eye on it!


Serving: 1serving | Calories: 235kcal | Carbohydrates: 24g | Protein: 9g | Fat: 13g | Saturated Fat: 6g | Polyunsaturated Fat: 0g | Monounsaturated Fat: 0g | Trans Fat: 0g | Cholesterol: 22mg | Sodium: 548mg | Potassium: 592mg | Fiber: 4g | Sugar: 7g | Vitamin A: 1041IU | Vitamin C: 16mg | Calcium: 165mg | Iron: 2mg