Step 1: Prepare the Chicken - Preheat your oven to 375°F (190°C). Place chicken breasts between plastic wrap and pound to an even thickness of about 1/2 inch.
Step 2: Make the Filling - In a mixing bowl, combine cream cheese, spinach, mozzarella, feta, milk, garlic powder, salt, black pepper, nutmeg, and cayenne. Mix until creamy.
Step 3: Stuff the Chicken - Place a portion of filling in the center of each chicken breast. Fold sides over and secure with toothpicks or kitchen twine.
Step 4: Bake the Chicken - Grease a baking dish, place chicken seam side down, and bake for 25-30 minutes until cooked through (internal temperature of 165°F).
Step 5: Serve and Garnish - Let chicken rest, remove toothpicks, slice, and serve garnished with halved grape tomatoes.
