01 - In a large skillet over medium heat, cook the ground beef, breaking it apart with a spoon, until fully browned and cooked through, approximately 5 to 7 minutes. Drain any excess fat from the skillet.
02 - Add the finely chopped onion to the skillet with the beef and cook until softened, about 2 minutes. Stir in the minced garlic and cook for an additional 30 seconds until fragrant.
03 - Incorporate the ground cumin, chili powder, smoked paprika, dried oregano, salt, and black pepper into the beef mixture. If using, add the diced tomato. Cook for 2 minutes, stirring to ensure the spices are well distributed. Remove the skillet from heat and set the seasoned beef aside.
04 - In a small saucepan, gently heat the refried beans over low heat, stirring occasionally, until they are warmed through and spreadable.
05 - Preheat your oven to 350°F. Arrange the corn tostada shells on a baking sheet. If desired, sprinkle the shredded cheese evenly over the shells and bake for 3 to 4 minutes, until the cheese is melted and bubbly. Alternatively, warm the shells without cheese if preferred.
06 - To construct each tostada, spread a generous layer of warm refried beans onto a prepared tostada shell. Follow with a portion of the seasoned beef mixture. If desired, sprinkle additional shredded cheese on top.
07 - Garnish the assembled tostadas with shredded lettuce, diced tomatoes, a dollop of sour cream, sliced jalapeños, and fresh cilantro. Serve immediately with a squeeze of fresh lime juice from the wedges.