Drizzle olive oil into a medium-sized pot. Add the onion, and garlic and stir to combine. Season with salt and pepper. Saute over medium heat for about 5 minutes, or until the onion is soft and translucent.
Cut the tomatoes into quarters and scoop out the seeds with a spoon. Dice tomatoes into 1 inch cubes. Stir in the diced tomatoes and increase heat to medium-high until it starts to boil. When the mixture boils, reduce the heat to medium and simmer for about 15 minutes, uncovered, until most of the water evaporates. Monitor closely, reducing heat if necessary and stirring often.
Add sun-dried tomatoes into a blender or food processor along with a ladle or so of the tomato sauce. Process until mostly smooth. Stir this mixture back into the tomato sauce in the pot.
Stir in the minced basil, oregano, salt, and pepper, and red pepper flakes. Continue cooking until mixture has reached desired thickness and then remove from heat.