1. Cut the turkey across the grain into 1/4 inch strips. Sprinkle it with the chili powder and cumin. Heat the oil in medium, preferably non-stick frying pan and cook the turkey and onion over medium heat, stirring often until the onion is nearly softened -- about 3 minutes. Add the garlic and cook for 30 seconds. Stir in the broth and tomato paste. Cover the pan and simmer over medium-low heat for 8 minutes. (The taco filling can be made early in the day and refrigerated. Reheat before proceeding.)
2. Heat the tortillas in a 35-degree conventional oven for about 6 minutes, or wrap in plastic wrap and heat in a microwave over for about 1 minute.
3. Assemble the tacos by spooning the filling into the center of the tortillas, then top with the salsa, lettuce, and cheese. Fold the edges over and serve.