Preheat the oven to Gas Mark 6, 200ºC, fan 180ºC. Put the squash and pepper slices on a baking sheet and toss with 2 tablespoons of olive oil, the rosemary and seasoning. Roast for 25 minutes or until browned at edges, then remove and set aside.
Heat another 2 tablespoons oil in a saucepan. Add the garlic and cook for 2 minutes, or until just golden. Add the tomatoes and a pinch of salt. Simmer on a medium heat for 5 minutes or until thick. Pour the thickened liquid into a large baking dish.
Slice the polenta into 2cm (¾in) thick pieces. Place half in a layer over the tomatoes. Cover with the peppers and squash, then the mozzarella. Top with the remaining polenta and drizzle with the last tablespoon of oil. Season well. Sprinkle with Parmesan.
Bake for 20-25 minutes or until golden and bubbling. Serve with some rocket leaves, if you like, and other vegetable sides.
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