In a large skillet, heat the olive oil over medium heat. Add the garlic and onion and gently sauté for 1-1½ minutes. Add the eggplant and zucchini, and cook for about 2-3 minutes. Add the peppers, tomatoes and water. Season with salt and pepper, add the chili pepper (optional) and stir. Cover with lid and cook until the vegetables have softened. While the sauce is cooking, bring a large pot of salted water to a boil. Add the penne pasta and cook until the pasta is al dente (tender but firm to the bite). Drain the pasta, combine it with the sauce in the skillet and stir over low heat until well combined. Garnish each plate with a few basil leaves and serve at once.