Chop tomatoes, bell peppers, and zucchini into small cubes and sauté them for a few minutes in the oil in a pan.
Crush garlic cloves and chop basil – add to the pan along with balsamic vinegar, salt, and pepper. Let everything simmer for 10-15 minutes.
Meanwhile, cook the tortellini according to the instructions on the package in lightly salted water.
Mash the now-soft tomatoes and zucchini lightly with a fork in the pan to make a coarse tomato sauce.
Drain the tortellini and toss them in the pan.
Slice mozzarella and place on top in the pan.
Place the pan in the oven for 6-7 minutes at 200 degrees Celsius (392 degrees Fahrenheit) – just until the mozzarella is melted. Serve with a bit of fresh basil on top.