Heat 4 tablespoons olive oil in a large frying pan or skillet over medium heat.
Add the chopped onions, chopped red bell peppers and 1 teaspoon salt; cook for 10–15 minutes, stirring occasionally, until softened.
Stir in the sliced garlic and 1 teaspoon dried oregano; reduce heat to low and cook for 5 minutes more.
Transfer the pan contents to a blender or food processor, add the canned diced tomatoes, 1 teaspoon sugar and 1/4 teaspoon black pepper, then puree to your desired consistency.
Return the blended sauce to the pan, bring to a gentle simmer and cook for 5–10 minutes to meld the flavors.
Meanwhile, bring a large pot of water to a boil, add 1 tablespoon salt, and cook the 14 oz pasta according to the package instructions until al dente.
Reserve one cup of the pasta cooking water, then drain the pasta in a colander.
Return the drained pasta to the pot, add the red sauce and 1 tablespoon extra virgin olive oil, and gently stir over low heat to combine; add a splash of reserved pasta water if the sauce needs thinning.