Preheat oven to 375°F

Slice onion

Add vegetable oil to skillet and preheat at medium heat

Brown and cook the chicken breasts in preheated skillet until the juices run clear

Add onion and cook until soft

Spray casserole dish with cooking spray

Add chicken and onion to casserole dish

Microwave broccoli according to package directions

Drain broccoli

Spoon broccoli over chicken and onion mixture

Sprinkle garlic powder over mixture (to taste)

Pour alfredo sauce over contents of casserole dish

Cover and bake 20 minutes in preheated oven

Serve