01 - Heat olive oil in a large skillet over medium heat. Add chopped onion and cook for 2 to 3 minutes until softened.
02 - Incorporate minced garlic and cook for an additional 30 seconds until fragrant.
03 - Add ground beef to the skillet, breaking it up with a spoon. Cook for 6 to 8 minutes until fully browned. Drain excess fat if necessary.
04 - Stir in chili powder, ground cumin, smoked paprika, dried oregano, salt, and black pepper. Cook for 1 to 2 minutes until spices are aromatic, then remove from heat.
05 - Meanwhile, heat refried beans in a small saucepan over low heat, stirring in water gradually until a creamy consistency is achieved. Keep warm.
06 - Preheat oven to 350°F. Arrange corn tostada shells on a baking sheet and bake for 3 to 5 minutes until crisp and heated through if using store-bought shells.
07 - Spread a layer of warm refried beans on each tostada shell. Top evenly with seasoned beef, shredded lettuce, diced tomatoes, cheese, sour cream, avocado slices, and chopped cilantro.
08 - Serve immediately accompanied by lime wedges.