Add the arrabbiata sauce to a 12-inch cast-iron skillet and top with the peppers. Add the meatballs, then bake until the meatballs are cooked through, 18 to 20 minutes. Remove the meatballs from the oven, then turn the oven to the broiler setting.
Sprinkle the crushed red pepper flakes over the meatballs, then lay a slice of mozzarella over the top of each meatball. Place under the broiler for 3 to 4 minutes to melt the cheese, watching closely so that nothing burns. Scatter over the torn basil.