1. Heat olive oil in large sauce pan over medium heat. Cook onion and garlic in the olive oil for 5 minutes until the onions begin to soften.
2. Add the tomatoes, Italian seasoning and salt and pepper to the onion mixture. Cook for 10-15 minutes, just until the tomatoes begin to break down, but still keep their shape.
3. Cook pasta as directed on package. If adding spinach, throw it in with the pasta just before it is ready to strain. The spinach will pretty much cook instantly in the pasta water. Spoon sauce over pasta and enjoy. Top with chili flakes, if desired.
Source of recipe: I wrote this recipe.