In a non-stick pan, heat the oil over medium heat. Add the onion, garlic, and oregano; season with salt and pepper. Cook, stirring occasionally, until the onion is tender and caramelizing on the edges, about 4-5 minutes. Add the eggplant and tomatoes, then sauté for 2-3 minutes.
Reduce the heat to medium-low and cover with a lid; cook for about 5-6 minutes or until the eggplant is soft. Generously season with salt and pepper to taste.