01 - Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté for 2–3 minutes until softened.
02 - Add garlic and cook for 30 seconds until fragrant.
03 - Add ground beef. Cook, breaking it up with a spatula, until browned and cooked through, about 5–7 minutes. Drain excess fat if needed.
04 - Stir in tomato paste, chili powder, cumin, smoked paprika, oregano, salt, black pepper, and cayenne. Cook for 1 minute to toast spices.
05 - Pour in beef or chicken broth. Simmer for 3–4 minutes until the liquid reduces and the mixture is saucy but not watery. Adjust seasoning to taste.
06 - Warm hard taco shells according to package instructions (typically 3–5 minutes in a 350°F oven).
07 - Fill each taco shell with a generous spoonful of beef mixture. Top with shredded lettuce, cheese, diced tomato, sour cream, olives, cilantro, avocado, and salsa as desired. Serve immediately.