In a large skillet, heat 1 tablespoon of oil over medium heat. Add the finely chopped onions and sauté until soft, about 3-4 minutes.

Stir in the minced garlic and cook for an additional minute until fragrant.

Add 1 pound of ground beef to the skillet, breaking it up as it cooks. Cook for 6-8 minutes until browned.

Stir in taco seasoning, 1/4 cup of water, and salt and pepper. Cook for 5 minutes until the mixture thickens.

In a separate saucepan, heat refried beans over medium heat until warm and smooth, about 3-4 minutes.

On each tostada shell, spread a layer of warm refried beans, followed by the seasoned beef mixture. Top with shredded lettuce, diced tomatoes, and cheddar cheese.

Add a dollop of sour cream and a spoonful of salsa or pico de gallo. Sprinkle with olives and cilantro as desired.