Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
To make the cheese taco shells, sprinkle the shredded mozzarella and cheddar cheese into four circles on the baking sheet.
Bake for about 7-10 minutes, or until the cheese has melted and the edges begin to brown.
Remove from the oven and let them cool for 2-3 minutes. Then, lift the cheese circles and drape them over the handle of a wooden spoon suspended between two cups or jars, forming a taco shell shape. Allow to cool completely to harden.
While the cheese shells cool, heat olive oil in a skillet over medium heat. Add the onion and cook until translucent, about 3 minutes.
Add the minced garlic and cook for an additional minute.
Add the ground beef, breaking it apart with a spatula. Cook until browned, about 5-6 minutes.
Stir in cumin, chili powder, paprika, salt, and pepper. Cook for another 2 minutes, then remove from heat.
Assemble the tacos by filling each cheese shell with the seasoned ground beef.
Top with diced avocado, cherry tomatoes, chopped cilantro, and a squeeze of lime juice. Add a dollop of sour cream if desired.
Serve immediately and enjoy your keto-friendly tacos!