Preheat the oven to 350 degrees F (175 degrees C).

Heat 1 tablespoon oil in a large skillet over medium-high heat. Add onion and cook, stirring, until browned, 5 to 7 minutes. Transfer to a plate.

Add remaining olive oil to the skillet; add eggplant and bell pepper. Cook, stirring, until softened, about 5 minutes. Add tomato, garlic, parsley, salt, and pepper; cook 2 to 3 minutes more. Return onion to the skillet. Adjust seasonings if necessary.

Transfer eggplant mixture to a baking pan. Bake in the preheated oven for 30 minutes.

Cool 1 hour; serve at room temperature or refrigerate and serve chilled.