In a large skillet (large enough to fit 1 tortilla) heat enough veggie oil to cover bottom of pan on med-high heat.(You want the oil to bubble when you place a tortilla in it.) Place tortillas, 1 at a time, in skillet. Once oil starts to bubble flip tortilla over. Tortilla will want to puff up now. When it does that, take it out and place it on a plate. Continue with rest of tortillas, making a pile on the plate.
Mix together cut up cooked chicken, diced onion, sour cream & 1 Cup of cheese.
Place in a line on tortilla, 1- 1&1/2 spoons of mixture. Roll up and place seam side down on 9x13" baking dish.
Pour enchilada sauce evenly over filled & rolled tortillas. Top with remaining 1 Cup cheddar cheese.