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.
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.