Heat the oil in a 3 quart saucepan over medium heat. Add the bell pepper, carrot, celery, onion and garlic. Saute until the veggies are soft, about 5 minutes. Add the tomato paste and cook for 1 minute, stirring constantly.
Add the tomatoes and reduce the heat to low. Simmer for 10 minutes.
Remove from the heat and puree with an immersion blender or run through a food processor in batches until almost smooth.
Return the sauce to the heat and add the oregano and thyme. Add salt and pepper to taste. Let simmer on low anywhere from 10 minutes to 2 hours. The longer you simmer the thicker and more flavorful the sauce will be.