01 - Heat olive oil in a large skillet over medium heat. Add chopped onion and cook for 2 to 3 minutes until softened. Add minced garlic and cook for an additional 30 seconds.
02 - Add ground beef to the skillet and cook, breaking it up with a spoon, until browned, about 5 to 7 minutes. Drain excess fat if necessary.
03 - Stir in ground cumin, chili powder, smoked paprika, dried oregano, salt, and black pepper. Add tomato paste and water; mix well and simmer for 3 to 4 minutes until mixture thickens.
04 - While the beef simmers, warm the refried beans in a saucepan over low heat, stirring occasionally.
05 - Spread a thin layer of warm refried beans over each tostada shell. Top evenly with the seasoned beef, shredded lettuce, shredded cheese, and diced tomato.
06 - Garnish with sour cream, jalapeños, fresh cilantro, and a squeeze of lime juice as desired. Serve immediately.