Begin by preparing your vegetables. Chop the eggplant, zucchini, yellow squash, bell peppers, and onion into bite-sized pieces. Dice the tomatoes and finely chop the garlic.

In your large pot or Dutch oven, heat the olive oil over medium heat. Add the onions and garlic, sautéing until the onions become translucent - about 5 minutes.

Add the bell peppers to the pot and continue to sauté for another 5 minutes, until the peppers start to soften.

Add the eggplant and squash to the pot, stirring to combine all the ingredients. Allow the mixture to cook for another 5-10 minutes, until the vegetables begin to soften.

Add the diced tomatoes to the pot along with the thyme, basil, bay leaf, salt, and pepper. Stir everything together.

Reduce the heat to low, cover the pot, and let the Ratatouille simmer for about 30 minutes. During this time, the flavors will meld together, and the vegetables will become tender.

After 30 minutes, uncover the pot and check the seasoning. Adjust with more salt and pepper if necessary.

Serve the Ratatouille warm, garnished with a sprinkle of fresh basil.