Preheat the oven to 280 degrees
In a large ovenproof pan or Dutch oven, drizzle two tablespoons of olive oil and cook the onions and garlic over a medium flame until the onions become translucent and the garlic golden
Add the celery, carrots, peppers, tomato sauce and diced tomatoes into the pan and cook until they soften and the mixture thickens. Add the basil, a dash of salt and pepper to taste and mix
Using a large spoon, smooth out the sauce around the pan so it becomes a base of sauce
Take the eggplant, zucchini, squash and layer them in any order you wish in a circle around the pan so it forms colorful rings that cover the sauce base
Drizzle olive oil over the ratatouille and sprinkle a dash of salt, pepper and some of the chopped basil
Cover in aluminum foil and bake for about 3 hours, or until the vegetables begin to soften
Afterwards, take the foil off and bake for about half an hour uncovered until the vegetables roast
Let sit for ten minutes and sprinkle some parmesan cheese to garnish
Serve and enjoy! You can either eat it as is or use it to accompany a side of rice