Warm tortillas: wrap stack in damp paper towel, microwave 45–60 seconds (or warm 20–30 seconds per side in a dry skillet); keep wrapped in a kitchen towel.
Heat oil in a large skillet over medium-high; add beef in an even layer, brown undisturbed 2–3 minutes, then break up and cook 4–5 minutes until no pink remains.
Push beef to edges; add onion, cook 2–3 minutes until soft, then garlic, 30 seconds until fragrant.
Sprinkle chili powder, cumin, paprika, oregano, salt, pepper, and cayenne over beef; stir and cook 1 minute until spices smell toasted.
Stir in tomato sauce, scraping up browned bits; simmer on medium-low 3–4 minutes until sauce thickens and clings to meat. Taste and adjust salt.
Drain excess fat; spoon ~2 tbsp beef into each warm tortilla, add toppings, and serve immediately.
