Heat the oven to 375ºF. Line a baking sheet with foil.
Coat a medium nonstick skillet with cooking spray and warm it over medium heat. Add the onion and pepper and cook until tender, 4 to 6 minutes. Stir in the garlic, oregano, cumin, and chipotle powder and cook for 1 minute. Stir in the turkey and barbecue sauce and cook until heated through, 2 to 3 minutes. Remove the pan from the heat.
Spread about a 13-by-9-inch rectangle of chips across the foil on the baking sheet. Scatter on one-third of the cheese, half of the turkey mixture, and half of the scallions. Repeat with one more layer of chips, turkey mixture, and scallions. Top with the remaining cheese.
Bake until the cheese melts and browns slightly, 12 to 15 minutes.
Tip: You can use almost any leftover meat in place of the turkey; good examples include shredded chicken, thinly sliced steak, or chopped pork. Look for tortilla chips and barbecue sauce that list the sodium content as less than 5 percent of the daily value per serving (less than 140 milligrams of sodium per serving). Good brands include Xochitl or Natural Tostitos for chips and Lum Taylor’s or Olde Cape Cod Honey Orange for barbecue sauce.