Place the tomatoes in a 13-by-9-inch baking dish. Toss the tomatoes with the olive oil, oregano and garlic. Season heavily with salt and pepper. Roast the tomatoes until fully cooked, about 40 minutes.
Once the tomatoes are cooked, place them in a blender and process until smooth. Check for seasoning and then serve.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.