In a large saucepan, heat the olive oil over medium heat. Add 3 garlic cloves and fry until lightly golden, about 5 minutes. Stir in the tomatoes and cook until heated through, about 5 minutes. Season the sauce to taste with salt, pepper, crushed red pepper and oregano. Add the chicken and simmer, stirring occasionally, until cooked through, about 10 minutes.
Meanwhile, preheat the broiler. Spread a little butter on each hoagie roll half, place cut side up on a small baking sheet and broil until golden and crunchy, about 3 minutes. Gently rub with the remaining garlic clove and set aside.
Distribute half of the mozzarella on the roll halves. Arrange the chicken and some sauce over the cheese and then top with the remaining cheese. Broil until the cheese is melted and bubbly, about 3 minutes. Sprinkle a bit of oregano on top and serve immediately.