In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 3-4 minutes.
Add the minced garlic and cook for an additional 1 minute until fragrant.
Add the ground beef to the skillet, breaking it apart with a spatula. Cook until browned, about 5-7 minutes. Drain any excess fat.
Stir in the chili powder, cumin, paprika, salt, and pepper. Cook for another 2-3 minutes to combine the flavors.
While the beef is cooking, preheat the oven to 350°F. Place the tostada shells on a baking sheet and warm them in the oven for about 5 minutes.
To assemble, spread a layer of refried beans on each tostada shell. Top with the seasoned ground beef, shredded lettuce, diced tomatoes, and shredded cheddar cheese.
Add a dollop of sour cream on top of each tostada and sprinkle with sliced jalapeños and fresh cilantro if desired.
Serve immediately and enjoy your crunchy beef tostadas!