Step 1Oil 2 (15x10-inch) jellyroll pans.
Step 2Heat 3 tablespoons of olive oil in a large skillet over low heat. Add the onions; cook, stirring frequently, until softened, about 20 minutes. Season with salt and pepper to taste and the oregano.
Step 3Spoon 1 cup of red chile sauce onto a wide dinner plate. Starting with 1 tortilla, dip both sides in the sauce. Place 1/2 cup of grated cheese, 2 olives and 1/3 cup of cooked onions down the middle of the tortilla. (We never added grated hard-boiled eggs, but many rancho families did.) Lastly, roll the sides of each tortilla over the filling. Place the enchilada, folded side down, on one of the pans. Repeat with the remaining tortillas. Pour the remaining red chile sauce over the enchiladas. Sprinkle the remaining cheese in a strip down the middle of each enchilada. Decorate with any remaining olives. Cover the pans and refrigerate the enchiladas until you are ready to bake them. Let them stand at room temperature 1 hour before baking.
Step 4Heat the oven to 350 degrees near serving time.
Step 5Bake the enchiladas until they are puffed and the cheese has melted, 20 to 25 minutes.