For rub, combine chipotle pepper, oregano, oil, cumin, salt, and garlic. Spread over surface of roast, rubbing in with your fingers. Cover and marinate in the refrigerator for 6 to 24 hours.
Place meat on a rack in a shallow roasting pan. Insert a meat thermometer into the center of roast. Roast in a 425 degree F. oven for 30 to 35 minutes or until thermometer registers 140 degrees F (Or, grill roast on the rack of an uncovered grill directly over medium coals for 35 to 40 minutes or until thermometer registers 140 degrees F)
Cover with foil and let stand 10 minutes before carving. Makes 6 to 8 servings.