01 - Heat olive oil in a large skillet over medium heat. Add finely chopped onions and cook for 2 to 3 minutes until translucent. Add minced garlic and cook for an additional 30 seconds until fragrant.
02 - Add ground beef to the skillet and cook, breaking it up with a spoon, until browned, approximately 6 to 8 minutes. Drain excess fat if necessary.
03 - Stir in chili powder, ground cumin, smoked paprika, dried oregano, salt, and black pepper. Cook for 1 minute to toast the spices, enhancing their aroma.
04 - Pour in tomato sauce and simmer for 3 to 4 minutes, stirring occasionally, until the mixture thickens and flavors meld. Remove from heat.
05 - In a separate saucepan, warm refried beans over low heat, adding water gradually to attain a spreadable consistency. Keep warm until assembly.
06 - Spread a layer of warm refried beans on each tostada shell. Top with the seasoned beef, then layer shredded lettuce, diced tomatoes, sliced red onion, shredded cheese, sliced avocado, and chopped cilantro.
07 - Drizzle each tostada with sour cream and serve alongside lime wedges to add a zesty finish.