1 Preheat the oven to 350ºF.
2 Make the sauce: In a blender, puree the garlic, onion, tomatoes, flour, chili powder, oregano, salt and water until smooth.
In a deep skillet over medium heat, heat the oil. Add the sauce and cook, stirring often, until it comes to a boil.
Lower the heat and cook the sauce at a steady simmer for 10 minutes. It may sputter like mad, so either stir often or top with a spatter guard. The sauce should have the consistency of heavy cream. Add more water to thin it if necessary.
Note: you may have a bit more sauce than you need. It can be stored in the refrigerator for up to 5 days and used for leftovers.
3 Bake the tortillas: Using a pastry brush, brush both sides of one tortilla with oil and place it on a plate. Set a second tortilla on top and brush the top with oil. Continue to brush and stack the tortillas in the same manner.
When done, press down on the stack gently so that that both sides of each tortilla are lightly coated with oil. This way, all the sides get covered with oil as you create the stack.
Spread them out on two baking sheets. Bake for 10 minutes, or until slightly crisp at the edges.
Note: You can prepare the tortillas up to a day ahead. Cool completely, then transfer to a plastic zip-top bag and store at room temperature.
4 Prepare the filling: In a microwave-safe bowl, combine the onion, corn, salt and pepper. Microwave for 2 minutes. Add the beans and microwave for one minute longer, or until the filling is hot all the way through. Cover and keep warm.
Note: The filling can be prepared up to a day ahead and refrigerated.
5 Assemble the enchiladas: Set 4 plates next to the stove.
Dip one tortilla in the sauce and set it on one of the plates. Spread 2 tablespoons of the filling over the tortilla. Dip a second tortilla in the sauce and place it on top. Spread with 2 more tablespoons of the filling. Dip a third tortilla in the sauce and place on top of the stack. Spoon a little more sauce over the top.
Sprinkle the stack with one-fourth of the cheese, one-fourth of the avocado slices, one-fourth of the radishes and top with one-fourth of the cilantro leaves.
Repeat with remaining tortillas, sauce, and garnishes.
If desired, transfer each stack to a baking sheet in a 350°F oven to keep warm as you finish assembling the rest. Serve all the stacks together at once.