Preheat oven to 425 degrees. Drizzle a large roasting pan with olive oil. Add chopped tomatoes, onion and garlic. Roast for about 30 minutes or until tomatoes begin to brown on edges.
Use a slotted spoon and transfer to your blender container, discard any pan juices. Blend until smooth.
Meanwhile in a large saucepan, cook your bacon in the olive oil. Once the bacon is cooked to your liking, remove it from the olive oil and reserve for another use.
Pour the sauce from the blender into the olive oil, add the oregano and red pepper flakes; bring to a simmer. Simmer for at least 30 minutes or up to 4 hours. Season with salt and pepper to taste.
If your tomatoes have lots of seeds, you can give them a squeeze to remove most. Don't worry about the skins, we're going into the blender at the end and it will take care of those. Makes about 4 cups.