Preheat oven to 375°F and grease a 9x13-inch baking dish.
Cut chicken into bite-sized pieces, season with garlic powder, salt, and pepper.
Sear chicken in olive oil for 3–4 minutes per side until lightly golden; transfer to dish.
In a large bowl, mix softened cream cheese, sour cream, and mayonnaise until smooth.
Stir in garlic, onion powder, red pepper flakes, spinach, and artichokes.
Spread creamy mixture evenly over the chicken in the baking dish.
Top with mozzarella and parmesan; add breadcrumbs if desired.
Cover with foil and bake 25 minutes; uncover and bake 15–20 minutes more.
Let casserole rest for 5–10 minutes before serving.