Drain and slice the red peppers, reserving 3 tablespoons of the oil.
Arrange half the polenta slices in a lightly buttered ovenproof dish and scatter over half the sliced peppers and cheeses.
Repeat the layers and cook in a preheated oven, 240°C (475°F), Gas Mark 9, for 15 minutes.
Meanwhile, heat the oil from the peppers in a pan and fry the garlic over a medium heat until soft and beginning to turn golden. Stir in the remaining ingredients, season to taste and bring to the boil, then reduce the heat and leave to bubble gently for 15–20 minutes.
Put the polenta bake under a preheated hot grill for 5 minutes to brown the top. Garnish with basil leaves and serve immediately with the tomato sauce.