In a medium-size frying pan, heat the olive oil. Add onion and garlic and saute until tender, about 4 minutes. Add pepper and oregano and cook 1 minute more, stirring constantly. Add the tomatoes and simmer for about 15 minutes, until sauce starts to thicken. Add salt to taste. Keep sauce warm until you are ready to serve it over freshly cooked pasta.
Canned tomatoes may have enough salt, but you might want to add 1/2 to 1 tsp. salt if using fresh tomatoes.