Preheat oven to 425°F (220°C) and place a rack in the middle. Rub a medium-large baking dish with a bit of olive oil and set aside.
Spread cauliflower florets in an even layer on a rimmed baking sheet. Drizzle over 1 tablespoon of olive oil and sprinkle with coarse salt and pepper. Roast in the oven for 30 minutes , turning once.
In the meantime heat tomato sauce and tomato paste in a large saucepan over low heat. Once warm, stir in heavy cream, Parmesan, red pepper flakes (if using), salt, and pepper.
Remove from the heat, and stir in the cauliflower.
Fold in half of the mozzarella, half of the tomatoes, and a pinch of the chopped basil.
Pour the entire cauliflower mixture into the prepared baking dish.
Top with remaining mozzarella and remaining tomatoes
Lower oven temperature to 350°F (175°C) and bake in the oven for 30 minutes.
Then turn the broiler on and broil for 1 to 2 minutes until the cheese is golden and bubbly.
Serve with fresh basil top of it.
