Preheat the oven to 350°F (180°C). Grease a large baking tray and set aside.
Place the tomato sauce, onion, garlic, and taco seasoning in a high speed blender. Blend until smooth. Pour into a bowl and set aside.
Place large pot or saucepan over medium heat. Add the oil and once hot, add the diced onions and peppers and cook for 2-3 minutes, until the onions are golden. Add the diced chicken and taco seasoning and mix well. Cook for 8-10 minutes, while stirring regularly, until the chicken is fully cooked.
Start assembling the enchiladas. Place a single tortilla onto a plate. Spread 1-2 tablespoons of enchilada sauce, or enough to cover the tortilla. Add some of the chicken filling into the center, followed by a few tablespoons of shredded cheese. Fold either together and use a toothpick to hold it in place. Place the filled tortilla into the baking dish. Repeat until all the tortillas are filled.
Cover the tortillas with any remaining enchilada sauce and sprinkle with the remaining cheese. Bake for 10-12 minutes, or until the cheese has melted. Remove the toothpicks and serve immediately.
Notes
Tortilla brands: I like Carb Balance or Mission.
Leftovers: Keep in the fridge for up to 5 days or the freezer for up to 6 months.
REHEATING: Enchiladas are best reheated in a preheated oven until the cheese is warm and the edges of the tortillas are crispy. You can reheat from frozen.