Preheat your oven to 225°F.

Prepare the toppings: Grate 1-1/2 cups of cheese. Dice one ripe tomato. Shred 1/3 of a head of iceberg lettuce. Pit, peel, and dice one ripe avocado. Place all of these and the sour cream into small serving bowls and set aside.

In a large skillet over medium-high heat, warm the oil. Add the onion to the pan and sauté until soft, approximately 5 minutes.

Add the jalapeño pepper and garlic to the onions and continue to cook until the garlic is fragrant, about 1 minute.

Stir in the chili powder, cumin, oregano, salt, pepper, and cayenne. Add the ground beef, break it up with a spoon, and cook until completely browned, approximately 8 minutes.

Spoon the warm beef mixture onto one half of each tortilla and top that right away with cheese so it starts to melt. Fold the tortillas over and serve them on a platter with the bowls of toppings.