Rinse the mushrooms, pat dry, and slice thick. Mince the garlic. Heat a large, deep skillet over medium-high heat with olive oil. Once the oil is hot, add the mushrooms and saute 5-6 minutes, or until they have softened and released all of their moisture.Remove from pan to a plate and cover to keep warm. Depending on the size of your skillet, you may need to do this in two batches.
Lower the heat to medium and add the butter. Once the butter is melted and bubbling, add the onion. Saute 3-4 minutes until caramelized. Then add in the garlic. Saute for 30 seconds.
Add the flour, stir well and cook for 1 minute.
Pour in the half and half and chicken stock. Whisking continuously until the butter flour mixture is no longer clumpy and the bottom of the pan has been deglazed from sautéing. Add the Italian seasoning, salt, and pepper.
Add in the orzo pasta and stir to combine. If it starts boiling, reduce the heat to medium-low and allow it to maintain a simmer.
Cook uncovered, stirring frequently to ensure the orzo does not stick to the bottom of the pan or together, until it is al dente and the liquid has thickened to form a creamy sauce. Apprximately 10-15 minutes, or according to the package instructions.
While the orzo is cooking, line the scallops up on a paper towel and pat them dry. Removing some of the water will help to crisp the outsides.Season the scallops with salt, pepper, and garlic powder.
Place a large cast iron skillet over medium heat with the butter. Once the butter is bubbling and starting to brown, add the scallops one at a time seasoned side down. Sear for 2-3 minutes on each side. Remove from pan to a dish and cover to keep warm.
Once the orzo is cooked and the sauce has thickened, remove from heat. Taste test and add additional seasonings, if needed.Stir in the baby spinach and parmesan cheese. Mix until the cheese has melted and the spinach has wilted. Stir in the mushrooms and top with scallops to re-warm both.
Serve garnished with freshly grated parmesan cheese, black pepper, and freshly chopped parsley.