• Preheat Oven: Preheat oven to 400°F (204°C). Lightly brush a 9x13-inch baking dish with olive oil.

Make the Enchilada Sauce

• In a medium saucepan, heat 3 tablespoons of olive oil over medium-low heat. Sprinkle in the flour and cook, stirring continuously, for about 1 minute until smooth and bubbling. Stir in the chili powder, ancho chile powder, oregano, and cumin; cook for 30 seconds until fragrant. Whisk in the broth and tomato sauce until smooth. Let the sauce come to a simmer and cook for 5 to 8 minutes, stirring frequently, until it's thick enough to coat the back of a spoon. Remove from heat and season with salt to taste.

Prepare the Tortillas:

• In a small, non-stick skillet, heat oil over medium heat until hot. Add one corn tortilla and fry for 10-15 seconds on each side until it's flexible and lightly browned; lift with tongs, shaking off excess oil, then transfer to a clean plate. Continue with the remaining tortillas, stacking them as you finish each one. Keep an eye on the heat level - adjust it if the tortillas are browning too slowly or too quickly and add more oil to the pan as needed.

Assemble and Bake:

• Brush bottom and edges of a 9 x 13-inch baking dish with olive oil. Spread 1/2 cup of enchilada sauce into dish in an even layer.
• Combine shredded Monterey Jack and cheddar cheeses in a large bowl; set aside 1 cup (~2 ounces) for topping. Sprinkle 1/2 cup cheese (~1 ounce) mixture and ~1 tablespoon of sliced green onion down the center of one warm tortilla; roll up and place seam-side down in the baking dish. Repeat process with the remaining tortillas, arranging in 2 columns of 6 enchiladas across the width of the baking dish.
• Pour remaining enchilada sauce evenly over the enchiladas and sprinkle reserved cheese over the top. Cover dish tightly with aluminum foil and bake until cheese melts and enchiladas are heated through, ~20 minutes.

Serve:

• Remove from oven and let stand 5 minutes before serving. Garnish with sliced green onion if you like and serve with your choice of toppings.