Heat 2 tablespoons olive oil in a Dutch oven over medium-high heat. Once hot, whisk in 2 Tablespoons all-purpose flour, 2 teaspoons chili powder, 1 teaspoon ground cumin, ½ teaspoon salt, ¼ teaspoon ground black pepper, and ¼ teaspoon dried oregano. Cook for 5 minutes, whisking often.
Whisk in the 3 Tablespoons tomato paste, then whisk in 2 cups chicken stock until there are no lumps. Simmer for at least 15 minutes, more is fine.
Heat another 2 tablespoons olive oil in a large skillet over medium-high heat. Add the diced 1 small onion and cook for 5 minutes until soft. Then add the minced 1 clove garlic and cook for 1 minute, stirring frequently.
Add the diced 1 pound boneless skinless chicken breast and saute this for 5 to 10 minutes or until the chicken is cooked through. Then stir in the 4 ounces green chilies and cook just until heated through.
Spoon just enough enchilada sauce to coat the bottom of the prepared baking dish.
Preheat the oven to 350°F.
Add the remaining 2 tablespoons olive oil to a skillet and heat over medium-high heat.
Lightly fry the 12 corn or flour tortillas in the oil one at a time for about 10 seconds per side. Then place them on paper towels to absorb excess oil.
Spread a little enchilada sauce on each tortilla and place about ¼ cup of filling down the center of each tortilla. Roll up the tortillas and place them seam-side down next to one another in the baking dish. Spread the remaining enchilada sauce over top. Sprinkle the 2 cups Mexican blend cheese evenly over the top.
Bake for 15 minutes or until the cheese is bubbly.
Serve hot with your favorite toppings.