Stir together first 4 ingredients; rub pork tenderloins evenly with seasoning mixture. Lightly coat pork with oil cooking spray.
Grill, covered with grill lid, over medium-high heat (350° to 400°) 10 to 12 minutes on each side or until a meat thermometer inserted into thickest portions registers 155°. Remove from grill, and let stand 10 minutes. Chop or slice, and serve on hamburger buns. Drizzle each sandwich with 1 Tbsp. Sweet Onion Barbecue Sauce.
Sweet Onion Barbecue Sauce:
Stir together all ingredients and 1/2 cup water in a large saucepan; bring to a boil over medium heat. Reduce heat to low, and simmer, stirring occasionally, 20 minutes.