Heat a skillet with 1 tablespoon of vegetable oil over medium-low heat. Add onions, 1/4 teaspoon of salt, and 1/4 teaspoon of pepper, and cook until onions begin to brown, stirring occasionally.
Increase heat to medium-high. Add ground beef, 3/4 teaspoon of salt, 3/4 teaspoon of pepper, and 1/4 teaspoon of garlic salt. Cook and stir, breaking the meat apart as you go, until the beef is thoroughly cooked.
Add diced potato, 1/2 teaspoon of salt, and 1/4 teaspoon of pepper. Stir and reduce the heat to low. Cover and cook for ten minutes. Stir and check the potatoes for doneness. If they are not done, cover and continue cooking until the potatoes are cooked.
Squeeze half a lime over the filling and stir. Taste and adjust seasoning if needed.
Line a plate with a paper towel and set aside.
Fill another skillet with 1/4 inch of vegetable oil and heat over medium heat. Carefully, lay one tortilla flat in the skillet. Spoon about 2 tablespoons of ground beef and potato filling on one side of the tortilla. Using tongs, fold the tortilla in half. Repeat until the skillet is filled with a single layer of folded tacos.
Cook until the bottoms are lightly browned. Flip and cook the other side until lightly browned.
Remove the tacos from the pan and place them on a paper-towel-lined plate. Repeat with remaining tortillas.
To serve, gently pry tacos open and fill with salsa, lettuce, cheese, and avocado.
