To make the sauce, heat the olive oil over medium heat in a medium saucepan. Add 1 rounded teaspoon cumin, 1 rounded teaspoon chili powder, flour and tomato paste, and cook while whisking for 1 minute.
Whisk in the broth and ¾ cup water, and bring the mixture to a boil. Reduce to a simmer, and cook until the sauce is slightly thickened, about 5 to 8 minutes. Season with salt and pepper, and set aside.
To make the filling, combine 1 cup of Monterey Jack, 1 cup of cheddar, the beans, spinach, corn, scallion whites, ¼ cup scallion greens and the remaining cumin and chili powder in a large bowl. Season with salt and pepper.
Preheat the oven to 400 degrees F, and lightly oil two 8-inch square baking dishes. Set aside.
Stack the tortillas in aluminum foil, wrap them up and heat them in the oven or 5 to 10 minutes.
Top each warmed tortilla with ⅓ heaping cup of filling. Roll the tortillas tightly, and arrange them, seam side down, in the oiled baking dishes.
Top the enchiladas with the sauce, and sprinkle on the remaining ½ cup of each kind of cheese, divided evenly between the baking dishes.
Bake, uncovered, until the enchiladas are hot and bubbly, about 20 minutes. Cool for 5 minutes, and then serve garnished with the remaining scallion greens.
