Pour tomatoes into a large bowl and crush, using your hands or a potato masher. *Note: They may not crush all the way down at first, and that's okay. After they have simmered for 5-10 minutes, they will soften.Pour 1 cup of water into the can (to get all of the tomato juice left in the can) and set that aside.
Heat the olive oil in a large skillet over medium heat. When the oil is shimmering and hot, add the garlic.
As soon as the garlic begins to sizzle (about 30 seconds), add the tomatoes and the reserved tomato water. Stir in the red pepper flakes and oregano. Taste the sauce, then season it with salt and pepper as desired.
Simmer tomato sauce until it is rich and has thickened, about 15 minutes. After 5-10 minutes, use a potato masher to crush the tomatoes futher. This helps to create a smoother consistency.Before removing the pan from the heat, be sure to taste the sauce and add more salt and/or pepper, if needed. Garnish with chopped fresh basil before serving, if desired.
Notes
Store San Marzano marinara sauce for up to 4 days in the refrigerator or in the freezer for up to 6 months.