Heat Oil: In a large cast iron skillet, heat vegetable oil over medium-high heat until it shimmers.

Brown Beef: Add lean ground beef to the hot skillet, breaking it apart with a spatula. Cook until fully browned.

Sauté Vegetables: Stir in diced sweet onion and bell pepper; cook until the onion turns translucent.

Combine Spices: Add tomato paste, minced garlic, smoked paprika, chili powder, and cayenne pepper to the skillet.

Create Sauce: Pour in beef stock, then mix in ketchup, Dijon mustard, Worcestershire sauce, and brown sugar.

Simmer: Bring mixture to a boil, then reduce heat to low and simmer uncovered.

Serve: Once thickened, remove from heat and serve the mixture on buns of your choice.