Heat the oil in a frying pan, add the onion and garlic and cook over a medium heat for 3 minutes until softened. Stir in the courgettes and red pepper and cook for 5 minutes until the courgettes have softened.
Stir the mascarpone into the pan until melted, then add the passata and simmer for 2–3 minutes. Season to taste with salt and pepper and stir in the basil.
Meanwhile, cook the pasta in a large saucepan of lightly salted boiling water for 3–4 minutes, or according to the packet instructions, until al dente. Drain and return to the pan.
Stir the sauce into the cooked pasta and toss well. Serve immediately with the basil scattered over.