In a large skillet over medium heat, brown the ground beef until fully cooked, about 5-7 minutes. Drain excess fat if necessary.
Stir in chili powder, cumin, garlic powder, onion powder, salt, and pepper. Cook for an additional 2-3 minutes until the spices are fragrant.
While the beef is cooking, preheat the oven to 350°F. Place tostada shells on a baking sheet and warm in the oven for about 5 minutes.
To assemble, spread about 2 tablespoons of refried beans on each tostada shell.
Top each tostada with a generous portion of the seasoned ground beef.
Add shredded lettuce, diced tomatoes, and shredded cheddar cheese on top.
Finish with a dollop of sour cream and sprinkle with black olives and cilantro if desired.
Serve immediately and enjoy your delicious tostadas!