Preheat the oven to 400 degrees Fahrenheit. Place the chicken breast in a baking dish or on a lined baking sheet.
Drizzle the chicken breasts with spicy pesto sauce. Place slices of mozzarella cheese and tomatoes on top of the chicken. Sprinkle with a pinch of salt, pepper, and red pepper flakes if desired.
Place the baking dish in the preheated oven. Bake for 15-20 minutes, depending on the thickness of the chicken filets, until the chicken is cooked through to an internal temperature of 165 degrees Fahrenheit.
Let cool for 3-5 minutes before serving warm with fresh basil leaves.