Heat the olive oil in a large skillet. Add the onion, bell peppers and garlic; saute for 5 minutes over medium heat. Add the zucchini and eggplant; saute 5 minutes. Stir in the salt and pepper; saute 2 minutes. Stir in the diced tomatoes and bring to a simmer. Allow the ratatouille to simmer for 30 minutes, stir in the basil 2 minutes before serving. Ratatouille may be served hot, cold or at room temperature. It excellent as a side dish, an entree, or tossed with pasta.