1. Instructions For Grilling
2. Preheat one side of grill to medium-high, the other side to medium-low.
3. In a nonstick saucepan over medium heat, add the olive oil. Saute onions in oil until soft, about 2 minutes. Stir in vinegar, ketchup, brown sugar, Worcestershire, Dijon and a little salt and pepper. Bring sauce to a boil, reduce heat and simmer until reduced to 1 ½ cups, about 10 minutes. Set aside 1 cup sauce for serving.
4. Brush turkey tenderloins with ¼ cup remaining sauce. Grill turkey, covered, on medium-low side of grill, 4 minutes. Flip turkey, base with 2 tablespoons sauce and grill 4 minutes. Baste again with 2 tablespoons sauce and transfer turkey to medium-high side. Cook basted turkey, until an instant read thermometer registers 165 degrees, about 4 minutes.
5. Remove turkey from grill and let rest for 5 minutes before slicing.
6. Drizzle remaining sauce that was set aside over turkey slices and serve.
7. Instructions For Baking
8. Preheat oven to 350 degrees. Place turkey tenderloins in a 9×9 baking pan. Cut pieces if too large. Reserve 1 cup sauce for serving and with remaining sauce, spread ¼ cup over top of tenderloins. Reserve ¼ cup for broiling.
9. Cover pan with foil and bake for 35-40 minutes.
10. Preheat broiler, cover cooked tenderloins with ¼ cup sauce and broil for about 3 minutes, until browned.
11. Remove turkey from oven and let rest for 5 minutes before slicing.
12. Drizzle the 1 cup sauce that was set aside, over turkey slices and serve.