In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 3 minutes. Stir in the minced garlic and cook for another minute.
Add the ground beef to the skillet, breaking it apart with a wooden spoon. Cook until browned and no longer pink, about 5-7 minutes. Season with cumin, chili powder, smoked paprika, salt, and pepper. Mix well and let it simmer for an additional 2-3 minutes to meld the flavors.
While the beef is cooking, prepare the tostada shells according to package instructions (usually baked or fried until crispy).
Spread a layer of refried beans on each tostada shell. Top with a generous amount of the seasoned ground beef mixture.
Layer on the shredded lettuce, diced tomatoes, avocado slices, and crumbled queso fresco on top of the beef.
Sprinkle fresh cilantro over the assembled tostadas and serve with lime wedges on the side for squeezing.