Preheat oven to 350 degrees F / 177 degrees C.
On silicone baking mat or parchment paper, lay out 1 cup cheddar cheese in four small circles, roughly ¼ cup per circle. Make sure cheese isn't overlapping to ensure that shells are crispy.
Bake for 6 to 8 minutes. Remove from oven when golden brown. Watch closely to prevent burning.
Let cool for 2 to 3 minutes. While still warm, fold over cheese, into taco shell shape. Shell should harden as it cools.
Fill four shells with ground beef, cheese, lettuce, sour cream, and avocado.
Serve and enjoy!