Rinse and halve the peppers. Remove the seeds and julienne. Rinse and quarter the tomatoes. Remove the seeds and cores, and chop.
Peel and finely chop the garlic and onion, then sauté in the oil. Add the peppers and tomatoes. Cover, and braise for 10 minutes over low heat, stirring occasionally. Season to taste with salt, pepper, and sugar. If you'd like, season with some vinegar. This can be served warm or cold.