Heat the oil in a medium pot or skillet. Once oil is shimmering, add the onions, celery, and carrots and cook until softened, 5-7 minutes. Add the red pepper flakes and garlic and stir until fragrant, about 30 seconds. Transfer the veggies to a blender and add the tomatoes and oregano. Blend until creamy.

If using and want warmer, pour the sauce back into the skillet used to cook the veggies and heat up. If saving, refrigerator for up to 1 week or in the freezer for up to 3 months.