In a blender, process half of the tomatoes until smooth, about 20 seconds. Transfer to a large bowl. Process the remaining tomatoes until mostly smooth but with some chunks, 4 or 5 pulses. Add to the bowl.

In a medium saucepan over medium, heat the oil, garlic, oregano and pepper flakes, stirring occasionally, until sizzling. Slowly pour in the tomatoes and stir. Bring to a simmer over medium-high, then reduce to low and cook, stirring occasionally and adjusting the heat as needed to maintain a simmer, until a wooden spoon leaves a trail when drawn through the sauce, 20 to 25 minutes.

Remove from the heat and let cool to room temperature. Taste and season with salt and pepper. Refrigerate in an airtight container for up to 3 days or freeze for up to 1 month (thaw and stir to recombine before using).