Cut the onions into wedges. Cut the bell pepper into wide strips. Cut the zucchini into large cubes. Finely chop the garlic and pluck the rosemary needles.
Mix the onions, bell pepper, zucchini and garlic with salt, pepper, rosemary and 2 tablespoons of oil and place on a baking sheet. Cook the vegetables at 200 ° C for about 20 minutes.
In the meantime, core and eighth the tomatoes.
After the 20 minutes add the tomatoes to the vegetables and let them cook for another 5 minutes.
Put the vegetables in a bowl. Chop the basil and pour it over the warm vegetables with salt, pepper, balsamic vinegar and the remaining olive oil. Mix well.