Preheat the oven to 350°F (175°C).
In a medium skillet over medium heat, add the olive oil, then whisk in the flour and chili powder and cook, stirring, until it becomes fragrant and begins to brown, about 1–2 minutes.
Slowly whisk in the tomato sauce and vegetable stock. Add garlic powder, onion powder, cumin, and salt and pepper to taste; continue whisking until the sauce begins to thicken, about 3–5 minutes.
Reserve 1 1/2 cups of the sauce in a bowl for topping.
Add the cooked diced chicken to the remaining sauce in the skillet and stir to coat and heat through.
Spoon about 2 tablespoons of filling and a little shredded cheese into the center of each tortilla, then roll up and place seam-side down in a 9×13-inch baking dish.
When all tortillas are arranged in the dish, pour the reserved sauce evenly over the top and sprinkle with the remaining shredded Colby Jack cheese.
Bake for 20–25 minutes, until the enchiladas are heated through and the cheese is melted and bubbly.
