In a medium skillet heat the olive oil over medium-high heat. Add the zucchini and cook until just starting to soften, about 5 – 7 minutes. Transfer to a paper towel-lined plate with a slotted spoon. Repeat this process with the eggplant and the red and yellow peppers (the peppers can be cooked together), adding more olive oil in between batches if the skillet seems dry. Set all vegetables aside.
In the same pan, add the onion. Sauté until it just starts to soften, about 5 minutes. Add the garlic and cook until fragrant, about 2 minutes. Add all of the vegetables back into the pan along with the tomato, tomato paste, bay leaf, parsley, thyme, salt and pepper. Stir to coat all the vegetables with the paste. Cover and cook over low heat until the tomatoes have softened and the flavors have had a chance to meld, about 15 minutes. Taste the ratatouille and feel free to add more salt or pepper if you like.
Remove and discard the bay leaf, parsley sprigs and thyme. Garnish with the fresh basil and serve immediately.
To skin a tomato, score an “x” in the bottom of the tomato and place in a pot of simmering water for 20-40 seconds or until you start to see the skin pull away at the edges. Transfer the tomato from the pot of water to an ice bath. You should be able to pull the skin off easily.