In a large skillet heat olive oil over medium heat. Add onion and cook for about 2 minutes, until translucent.
Add ground beef and brown. Using a potato masher, mash meat so you have small pieces of meat with no big chunks. Drain off excess grease.
Add garlic salt, pepper, tomatoes, and potatoes and cook over low heat for about 15 minutes, until potatoes are done. Salt to taste.
Heat 1-inch oil in a heavy-bottomed skillet.
Fry tortillas, one at a time, by folding in half and laying one half flat in oil while holding other half with a fork or tongs, and repeating with the other half to form a half moon shell, until golden and crisp, 1 to 2 minutes per side. Place taco shells on a paper towel lined plate. Repeat with remaining tortillas.
Spoon picadillo into each taco shell, and garnish with lettuce, tomato, salsa, cheese, and avocado if using.
Nutrition facts do not include optional toppings.
Can I use a different protein? While I grew up eating picadillo de res (res means "beef"), you can certainly swap in ground turkey, ground chicken, or ground bison if you prefer!
Can I use canned diced tomatoes? Sure, just be sure to drain them first!
How long does picadillo last? Use within a week, or toss any leftovers in the freezer for up to 3 months.