Heat the olive oil in a large saucepan over medium heat. Add the red pepper flakes and let them infuse the oil for about 2 minutes.
Add the minced onion to the pan and sauté until softened and translucent, about 5 minutes. Stir in the minced garlic and cook for 1 minute.
Add the whole peeled tomatoes, breaking them up with a spoon. Season with salt and sugar. Reduce the heat and cook for 30-40 minutes.