Make the sauce. In a small bowl, whisk tomato paste, vinegar, water, spices, salt, and sweetener until smooth. Adjust thickness with a splash more water. Set aside to let flavors meld.

Mix the taco seasoning. Combine all dry spices in a small bowl. Taste a pinch to ensure salt and heat levels feel right for you.

Cook the beef. Heat a skillet over medium-high. Add a drizzle of oil and the ground beef. Break it up with a spatula and cook until browned with a few crispy bits, about 6–8 minutes. Drain excess fat if needed.

Season and simmer. Sprinkle the taco seasoning over the beef. Stir in 1/3 cup water or broth. Reduce heat and simmer 2–3 minutes, stirring often, until thick and glossy. Taste and adjust salt.

Prep toppings. Shred lettuce, dice tomatoes and onions (if using), shred extra cheese, and slice jalapeños. Cut lime into wedges.

Choose your shells. Low-carb tortilla shells: Preheat oven to 375°F (190°C). Brush tortillas lightly with oil. Drape over two rungs of your oven rack to form a taco shape and bake 5–8 minutes until crisp. Watch closely to avoid over-browning.

Cheese shells: Line a sheet pan with parchment. Make 4–6 mounds of shredded cheddar (about 1/3 cup each), spread into 5-inch circles. Bake at 375°F (190°C) for 6–8 minutes until bubbling and just turning golden at edges. Let rest 30–45 seconds, then gently drape each over a wooden spoon handle or the side of a loaf pan to set into a shell.

Assemble. Add seasoned beef to each shell. Top with lettuce, shredded cheese, a small sprinkle of tomato and onion, and drizzle with the hot sauce. Add sour cream or avocado if you like. Finish with a squeeze of lime.

Serve right away. These are best while the shells are crisp and the beef is warm.