Marinate Chicken: To a freezer bag, add chicken, 1 Tablespoon avocado oil, minced garlic, Italian seasoning, pepper, salt, paprika, and red pepper flakes. Seal bag and, using hands, shake and massage mixture into chicken until marinade ingredients are well-combined. Transfer bag to refrigerator to marinate.
Preheat Oven: Place oven rack in middle of oven, preheat oven to 450 degrees F, and coat 9x13-inch baking pan with nonstick cooking spray.
Wilt Spinach: While oven preheats, in a pan on the stovetop over medium heat, heat remaining 1 Tablespoon avocado oil. Add spinach and allow to wilt and for excess liquid to cook off, then remove pan from the heat and set pan aside.
Prepare Chicken Bake: Unseal bag of marinated chicken and, using tongs, transfer chicken to prepared baking pan. Using a knife, spread softened cream cheese atop chicken pieces and then, using tongs, lay spinach atop cream cheese. Sprinkle shredded mozzarella on top.
Bake: Transfer pan to oven to bake until chicken has reached an internal temperature of 165 degrees F, about 20-22 minutes.
Garnish and Serve: Remove pan from oven, garnish with pepper and paprika, then serve.