Place chicken breasts in 10.5 x 7.5 casserole pan. Drizzle with olive oil and sprinkle lightly with salt and pepper.
Bake on the middle rack for 15 minutes.
Remove and add broccoli florets to the baking dish. Return to oven for 15 more minutes (or until chicken is fully cooked - internal temp of 165 degrees F. I recommend using an internal meat thermometer).
Remove from oven and place chicken breasts on a large plate to rest for 5 minutes. Then cut into 1 inch pieces.
Place spaghetti squash, cubed chicken, and Alfredo sauce to the casserole dish along with the broccoli and mix together.
Place back in the oven for 20-30 or minutes, or until bubbly.
Remove and serve immediately.
Notes
Casserole dish: option to use a 9x13 baking dish, it will still work just fine!