Ratatouille is a combination of bell peppers, eggplant, zucchini, and tomato—produce that peaks at the end of summer. The result is a massive batch of vegetables that keeps well for days. Serve as a side for proteins like steak or chicken.
Heat 3 tablespoons oil in a large pot over medium-high. Add bell peppers, onions, garlic, and ½ teaspoon salt; cook, stirring often, until slightly softened, 6 to 8 minutes. Transfer to a large bowl.
Add 4 tablespoons oil to pot. When oil is shimmering, add eggplants and cook, stirring often, until slightly softened, about 5 minutes; transfer to bowl with bell peppers.
Add remaining 3 tablespoons oil to pot. Add zucchini and ½ teaspoon salt; cook, stirring often, until slightly softened, about 5 minutes.
Add bell pepper mixture, oregano, and thyme to pot; stir to combine. Cover, reduce heat to medium-low, and cook, stirring halfway through, until tender, 10 to 12 minutes.
Stir in tomatoes and ½ teaspoon salt; cook, covered, until tomatoes burst, 8 to 10 minutes. Uncover and stir in vinegar, black pepper, and remaining ¾ teaspoon salt.