Preheat an outdoor grill to medium heat.
Brush the pork tenderloins with oil. Season generously with salt and pepper.
Use a clean cloth or rolled paper towels soaked with oil to season the grill. Grill the tenderloins, turning as necessary to mark them well on all sides. Use a basting brush to coat the tenderloins with sauce. Turn the tenderloins about every 2 minutes and reapply sauce to ensure even caramelization. Cook until an instant-read thermometer inserted in the center registers 145 degrees F (for medium doneness) to 160 degrees F (for well done).
Remove the tenderloins to a wire rack or plate to rest. Rest in a warm place for at least 5 to 7 minutes. Bring leftover sauce to a simmer and cook for 5 minutes. Slice and serve with sauce for dipping or drizzling.
Prickly Pear Tequila BBQ Sauce:
3 medium red onions, 2 whole, 1 minced
1 tablespoon canola oil
3/4 cup frozen prickly pear cactus puree, thawed
3 tablespoons unsalted butter
1/2 teaspoon coriander seed, freshly toasted and ground
1 1/2 teaspoons cumin seed, freshly toasted and ground
1 teaspoon crushed red pepper flakes
2 serrano chiles, ribs and seeds removed, minced
3 garlic cloves, minced
1 teaspoon lime zest
1/2 cup white Worcestershire sauce
1/2 cup tequila
1/4 cup apple cider vinegar
2 tablespoons lime juice
3/4 cup water
2 teaspoons kosher salt
Coat the whole red onions with canola oil and roast until inside layers are very soft, about 1 hour. Peel the onions and discard outer layers if blackened. Place in blender with prickly pear cactus puree and blend at high speed until completely smooth.
Preheat oven to 350 degrees F.
Heat 1 tablespoon of butter in a saucepan over medium heat. Saute minced onions until lightly caramelized, about 5 minutes. Add coriander, cumin, pepper flakes, serrano, garlic, and lime zest. Cook until fragrant, about 2 minutes.
Add Worcestershire, tequila, cider vinegar and lime juice. Cook over medium-high heat until reduced by half.
Stir in onion/cactus fruit puree, water and salt, to taste, and bring to a simmer.
Remove from heat and swirl in the remaining butter. The sauce may be blended to achieve a smoother consistency or left as it is.