In a large skillet, heat the olive oil over medium heat. Add the diced onion and minced garlic, sautéing until the onion becomes translucent.
Add the ground beef to the skillet, breaking it apart with a spatula. Cook until browned, about 5-7 minutes.
Stir in the chili powder, cumin, smoked paprika, salt, and pepper. Cook for an additional 2-3 minutes until the spices are well incorporated, then remove from heat.
Preheat your oven to 375°F (190°C). Place the tostada shells on a baking sheet and warm them in the oven for about 5 minutes until crispy.
Once the tostadas are warm, spread a layer of refried beans on each shell, followed by the seasoned ground beef mixture.
Top each tostada with shredded lettuce, diced tomatoes, and crumbled queso fresco.
Drizzle sour cream over the top and add avocado slices. Garnish with fresh cilantro.
Serve the tostadas with lime wedges on the side for an extra burst of flavor.