Preheat oven to 375 degrees and spray a 9" x 13" casserole dish with cooking spray. Season both sides of chicken breasts with salt and pepper and lay them in the casserole dish.

Drain artichoke hearts in a colander, pressing to remove as much liquid as possible, then chop them coarsely and scatter them on top of and around chicken breasts.

In a separate bowl, stir cream cheese until no lumps remain. Drain spinach in a colander and press very firmly to remove as much liquid as possible. Chop spinach coarsely and stir it into cream cheese.

Add Greek yogurt, garlic powder and Parmesan cheese then stir until completely combined. If mixture is extremely thick, add a tablespoon or two of milk to achieve a thick, but spreadable consistency. (This will largely depend on how well the spinach was drained and what type of cream cheese you’ve used.)

Spoon spinach mixture across the top of the chicken. (The spinach mixture will spread as it bakes.) Sprinkle evenly with mozzarella or Monterey jack cheese and crushed red pepper flakes, if desired.

Bake 35–40 minutes until top is golden brown and bubbly and chicken is cooked through. Remove from oven and allow chicken to rest 5 minutes before serving.