Fry the garlic and chilli in the olive oil until soft. Add the tomatoes and sugar. Season with salt and pepper and simmer uncovered for about 15 minutes, stirring often, until the tomato sauce has reduced and thickened.
Preheat the oven to 220C.
Place the mushrooms cap side down on a lightly greased baking sheet
Spoon the tomato sauce inside the mushrooms caps and spread the sauce to cover the cap
Tear the Mozzarella into small pieces and dot the tomato sauce with 2 thirds of the cheese
Top the mushrooms with your preferred topping ingredients and dot with the remaining cheese
Place in the oven and cook for about 15 minutes until the mushrooms are cooked through and the cheese melted
Set the oven to grill and grill the mushrooms for a few extra minutes until the cheese bubbles to a golden brown