ON STOVETOP:
In a medium saucepan heat olive oil. Add chopped bell pepper, onion and garlic. Saute for ~5 minutes. Then add eggplant and saute for 5 minutes more. Now add tomatoes (with the liquid), tomato paste, sugar and water. The water amount may vary depending on how much liquid your tomatoes had and how runny you like your sauce. Cook for additional 5 minutes until everything is soft.
IN MICROWAVE:
In a microwave safe dish combine onion, garlic and bell pepper. Sprinkle with oil, stir, cover and cook for 4 min on 70%. Add eggplant and water and cook for 5 more minutes on 70%. Add tomatoes, tomato paste and sugar. Return to microwave for 4 more minutes. Add salt and pepper to taste. You can go crazy here and add oregano or basil, but it's very good as it is. Now you can serve it (if you like chunks) or blend until smooth.