Preheat the oven: Get your oven started by preheating it to 180°C (350°F). This ensures everything cooks evenly.

Prepare the eggplant: Slice the eggplant into rounds or cubes, whichever you prefer. Thicker slices will take a little longer to bake, so keep that in mind. Lightly brush or drizzle the eggplant with olive oil to coat them for roasting. Season them generously with salt and pepper.

Bake the eggplant: Place the seasoned eggplant slices on a baking sheet and pop them in the preheated oven. Bake for 10-15 minutes, or until the eggplant slices become tender.

Sauté the vegetables: While the eggplant bakes, heat some olive oil in a pan over medium heat. Sauté the chopped onion and garlic until they soften and become fragrant. This will take about 3-5 minutes.

Add the bell peppers: Once the onion and garlic are softened, add the chopped red and yellow bell peppers to the pan. Cook them for an additional 5 minutes, or until they start to soften slightly.

Combine the sauce: Stir in the chopped tomatoes, tomato paste, and chopped fresh basil. Season the mixture with salt and pepper to your taste. Let the sauce simmer for a few minutes to allow the flavors to meld and thicken slightly.

Assemble the gratin: In a baking dish, create a layer with the pre-cooked eggplant slices. Top them with the flavorful vegetable sauce you just prepared.

Cheese time! Finally, sprinkle the combined grated cheese (cheddar, parmesan, or your choice) and shredded mozzarella cheese over the top of the gratin. The cheese will create a delicious and visually appealing topping.

Bake until bubbly: Place the assembled gratin back in the preheated oven and bake for 20-30 minutes. You'll know it's done when the cheese is melted, golden brown, and bubbly.

Serve and enjoy! Once the gratin is cooked through, take it out of the oven and let it cool slightly before serving. Garnish it with a sprinkle of fresh parsley and dill for an extra touch of flavor and color. Enjoy this warm and comforting vegetarian dish!