Preheat the oven to 375ºF and spray a 9x13-inch casserole dish with non-stick cooking spray.
Then, heat a large dutch oven over medium/high heat. Add olive oil and butter.
When olive oil and butter are fragrant add the mushrooms to the dutch oven to give them time to cook down before adding the other vegetables. Saute mushrooms for 3-4 minutes.
Add onion, garlic, celery, carrots, garlic powder, and onion powder to the dutch oven and cook for an additional 3-4 minutes.
Next, make the roux. Sprinkle flour over the vegetables and use a wooden spoon to mix the flour with all of the vegetables until the flour absorbs all of the excess liquid in the pot. It should form a brown paste on the vegetables.
Turn heat to medium and slowly add the milk to the pot, stirring constantly until milk thickens. Remove from heat and set aside.
Add minute rice, frozen peas, and diced chicken to the greased casserole dish and mix.
Then, add the contents of the dutch oven to the casserole dish and mix again.
Add the chicken broth, black pepper, and salt to the casserole dish and mix until everything is combined.
Cover the casserole dish with tin foil and place in the oven. Bake at 375ºF for 30 minutes.
At 30 minutes, remove the tin foil and bake for an additional 20-25 minutes or until all of the liquid is absorbed.
Remove casserole dish from the oven and let sit for at least 10 minutes to fully thicken.
Serve with a biscuit and freshly ground black pepper and enjoy!