To the Instant Pot, add 3 tablespoons of butter. Select the 'Saute' option. Once the butter has melted and is bubbling, add the onions and mushrooms. Allow to cook 3-4 minutes, or until the onions are translucent.
Add in the minced garlic and cook 30-60 seconds, or until fragrant. Add chicken broth to the pot to deglaze. Using a wooden spoon, scrape along the bottom of the pot to remove any brown bits that have collected. This will help to prevent a "burn" notice during cooking. Cancel the saute option.
Season chicken breasts with salt and pepper, both sides. If chicken is thickly cut, butterfly/slice in half. Add chicken and seasonings: garlic powder, onion powder, Italian seasoning, and additional salt and pepper, as desired.
Select the 'Pressure Cook' button and select HIGH. Set the timer for 8 minutes.
When the timer goes off, do a safe quick release. I like to place a dish towel over the nozzle.
Check the thickest part of the chicken breast to ensure that it has been cooked through. The internal temperature should read 165 degrees F until a meat thermometer. If it is not fully cooked, remove from pot and shred with two forks. Return to the pot. If fully cooked, remove the chicken from the pot and shred using two forks. Cover to keep warm.
Break the pasta in half and add to the pot in a criss cross pattern to prevent clumping. Pour 1/4 cup of water overtop. The liquid needs to rest at or above the pasta.
Place the lid back on the pot, set the valve to the sealed position. Select the 'Pressure Cook' button and select HIGH. Set the timer for 4 minutes.
When the timer goes off, allow for a natural 3-4 minute release, followed by a quick release.
Cancel the auto 'Keep Warm' option and select the 'Saute' option. Stir the pasta. Add in the half and half, cream cheese, parmesan cheese, and mozzarella cheese. Stir to fully mix and allow the cheeses to melt.
Once the cheeses have melted, add the chicken back to the pot to warm, along with the peas.
While the cheeses are melting, place a medium nonstick pan over medium-low heat. Add the butter and once melted and bubbling, add the breadcrumbs to toast. Cook, stirring frequently, until the breadcrumbs are a light golden brown. *You can season the breadcrumbs with Italian seasonings, salt and pepper, all to taste.
Garnish pasta with breadcrumbs, freshly grated parmesan cheese, and freshly chopped parsley.