In a large skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until the onion becomes translucent, about 3-4 minutes.
Add the ground beef to the skillet, breaking it up with a wooden spoon as it cooks. Cook until browned, about 5-7 minutes.
Stir in the cumin, chili powder, salt, and pepper. Mix until the beef is evenly coated with the spices, then let it cook for an additional 2 minutes to allow the flavors to meld.
While the beef is cooking, prepare your tostada shells according to package instructions if they need to be baked or fried.
Once the beef is ready and the tostada shells are prepared, begin assembling the tostadas. Start by placing a generous layer of the seasoned ground beef on each tostada shell.
Top each tostada with shredded lettuce, diced tomatoes, and a sprinkle of grated cheese.
Finish with a dollop of sour cream or Greek yogurt on top, and garnish with fresh cilantro.
Serve the tostadas with lime wedges on the side for a fresh squeeze of flavor just before eating.