In a large sauce pan, heat the oil until shimmering. Cook the onion until it starts to go clear. Add the tomatoes, herbs, and pepper flakes. Season to taste with salt and pepper.
Simmer the sauce for 20 minutes, covered, stirring occasionally. Serve over pasta or use as you would any marinara sauce.
Notes
Note: to freeze, divide the sauce into meal-sized portions, chill completely, and store in the freezer for up to 3 months. To serve, thaw and reheat.