Heat a large skillet over medium-high heat. Add a touch of oil, swirl to coat, and cook the onions and garlic with a little pinch of salt just until they become fragrant and translucent.
Season with cumin and red chile to taste. Use as much as you'll want on the meat, not just the onions.
Crumble the meat into the pan. Stir to combine, breaking it up as you go, and cook through.
If you're using taco shells, line them up in a baking dish and distribute the meat mixture evenly. Top with cheese and park in an oven on low to help it melt. If you don't have an oven, you can use aluminum foil.
If you're using fresh tortillas, you'll assemble your tacos immediately before eating. Wrap the tortillas in foil and heat them in your oven or toaster oven on low while you cook the meat.
Top with salsa and enjoy. Some people add shredded lettuce and sour cream; you can if you want but I don't go in for that fluffy nonsense.