Preheat the oven to 350F. To make the sauce, whisk the oil and flour in a medium saucepan set over medium-high heat. Whisk in the chili powder, cumin, garlic, salt and pepper.
Whisk in the chicken stock (I free-poured, feel free to do the same) and tomato sauce and whisk until the sauce bubbles and thickens. Let it simmer for at least a minute, and add a little more stock if you'd like to thin it out - it should have the consistency of thin gravy.
To assemble the taco-enchiladas, spread a spoonful of the sauce in a line on the bottom of each corn tortilla and top with a spoonful of black beans, spreading it in a line over the sauce, and then the shredded chicken and a sprinkle of cheese. Roll them up (without tucking in the ends like you might with a burrito) or just fold them in half, like a taco, and line them up right beside each other in a 9x13-inch baking dish. Pour the remaining sauce overtop (I held some back - but add as much as you like) and sprinkle the top with green onions and the remaining cheese. Bake for 20 minutes, or until bubbly and golden. Serves 4-6.