Easy Homemade Marinara

In a large, deep skillet over medium heat, heat oil. Add onion and cook until soft, 5 minutes. Stir in garlic and cook until fragrant, 1 minute more.  Pour in tomatoes and use a wooden spoon to break tomatoes into chunks. Fill tomato can almost halfway with water and swirl to catch any remaining sauce, then add to skillet. Season with oregano, red pepper flakes, salt, and pepper and stir in basil. Bring mixture to simmer.  Reduce heat to low and simmer until liquid has reduced slightly, about 20 minutes. Discard basil before serving.