For the enchilada sauce: In a small saucepan over medium heat, add oil and flour. Stir in tomato paste, cumin, oregano, chili powder, salt, and pepper. Add water and bring sauce to a simmer. Cook for 10-15 minutes until sauce thickens, stirring occasionally. Remove from heat and set aside.
In a bowl, combine shredded chicken, salsa, cilantro and chopped onion.
Mix the jack and cheddar cheese together in a second bowl.
Steam corn tortillas in the microwave for 30-45 seconds to make them soft and easier to work with so they don't break.
Pour about a third of enchilada sauce in the bottom of a large baking dish.
Lay out tortillas flat and place a small handful of the cheese mixture in each tortilla, leaving about 1 cup for topping.
Evenly spread the shredded chicken among the tortillas. Then roll the tortillas up and place them in your baking dish. Evenly pour the remaining enchilada sauce on top of the enchiladas. Sprinkle top with remaining cheese.
Cover enchiladas with foil and bake in the oven for 25 minutes. Remove foil and cook for another 10-15 minutes until top is golden and bubbly.
Remove from oven and let cool. Sprinkle with chopped cilantro and a drizzle of sour cream. Enjoy!
If you are in a hurry, you can use canned enchilada sauce. You'll need about 2 cups or 16 oz.