1. Shell the peas, remove any excess parts, and rinse. Bring a large quantity of salted water to a boil and add the green beans. Cook for 2 minutes, then drain and set aside.
2. Chop the tomatoes and rinse the peas. Rinse the zucchinis, cut off the ends, and slice them into strips. Clean the carrots, peel them, and cut off the ends. Blanch them in salted water for 2 minutes, then drain and set aside.
3. Cook the sliced onion and clove of garlic in olive oil in a large saucepan until they are translucent. Add the zucchinis and carrots, peas, green beans, a pinch of salt and pepper, and stir occasionally with a wooden spoon for 5 minutes. Add the tomatoes and continue cooking for 15 minutes.
4. Just before removing the saucepan from the heat, clean and dry the basil, then chop it into thin strips. Add some of it to the sauce and mix.
5. Meanwhile, cook the shells in a large quantity of salted water until they are al dente. Drain, add the sauce, and garnish with the remaining basil. Serve immediately.