In a large skillet, heat a drizzle of oil over medium heat. Add the chopped onion and minced garlic, sautéing until softened, about 2-3 minutes.
Add the ground beef to the skillet, breaking it apart with a spoon. Cook until browned, stirring occasionally.
Stir in the chili powder, cumin, paprika, salt, and pepper. Cook for an additional 5 minutes, allowing the spices to meld into the beef. Remove from heat.
To assemble the tostadas, spread a layer of refried beans evenly onto each tostada shell.
Spoon the ground beef mixture on top of the beans, ensuring even distribution.
Generously sprinkle shredded lettuce and diced tomatoes over the beef.
Top each tostada with a handful of cheese and a dollop of sour cream.
Finish with a sprinkle of chopped cilantro for a fresh touch.
Serve with lime wedges on the side for an extra zesty flavor.