Combine chili powder, cumin, salt, oregano and garlic into a small mixing bowl. Place mixture over meat, pressing into surface.
Arrange coals for indirect cooking or if you are using a gas grill, place on low setting.
Place meat on grill, cover and grill for 30-45 minutes or until thermometer registers 160 degrees.
Spray onion slices with olive oil cooking spray and place on the grill rack over the coals (if using gas grill, place on sides of grill where you will not direct heat) for 10-15 minutes.
Slice pork and serve with grilled onions.
Nutritional facts:
Calories: 152
Calories from fat: 39
Percent total calories from:
Fat 26%, Protein 65%, Carbohydrates 10%