Pour the passata into a saucepan. Set over low heat.

Chop the cauliflower into small pieces. Also chop the onion. Sauté them over fairly high heat in a large frying pan with 2 tbsp olive oil, along with the pepper and salt, until nicely golden brown. Add the cauliflower to the sauce, let it simmer for another 5 minutes, and season further to taste.

Cook the pasta al dente according to the package instructions. Drain and reserve a little of the cooking water to thin the sauce to your liking.

Tear the mozzarella into small pieces. Serve the pasta with the sauce and finish the plates with pieces of mozzarella.