Heat 1 tbsp oil in a large skillet over medium-high heat. Add the beef, onion, and a pinch of salt. Cook, breaking up the meat, until no longer pink, about 5 minutes. Stir in the garlic, cook 1 minute, then add the taco seasoning and 2 tbsp water. Simmer until the liquid nearly evaporates, 2 to 3 minutes.

Microwave the tortillas wrapped in a damp paper towel for 30 seconds until pliable. Spoon 2 to 3 tbsp of beef and a sprinkle of cheese onto half of each tortilla, then fold over and press gently.

Wipe the skillet, return to medium heat, and add enough oil to coat the bottom (about 2 tbsp). Fry the folded tacos in a single layer, about 2 minutes per side, until golden and crisp. Drain on paper towels.

Gently open each taco with a butter knife and stuff with lettuce, sour cream, and salsa. Serve hot.