In a medium pot, heat the oil over medium heat and add the ground beef. Flatten into an even layer and cook undisturbed until it develops a brown crust. Then break it apart with your spatula to continue cooking.
Add the chopped onions and bell pepper. Saute until they are soft and the onions just begin to turn golden, 3-4 minutes. Add the garlic for a minute and then add the tomato paste and saute for another minute or two.
Add ketchup, mustard, maple syrup, apple cider vinegar, Worcestershire, chili powder, and salt. Stir to combine. Simmer until the sauce thickens a bit, 3-5 minutes more.
Serve inside burger, sandwich, or slider buns.
To Store for Later
Transfer the filling to a storage container with a sealable lid. Store in the refrigerator or your cooler for up to four days.
To Prep at Camp
Reheat the mixture in a pot on your camp stove or over the campfire. You may need to add a little water to bring back the sauciness. Serve on toasted buns with whatever toppings and sides you love!
Notes
Serving Size: This makes enough filling for 4 full-sized sandwiches or 6 sliders. (Nutrition info is based on 4 servings.)