Preheat your grill or grill pan over medium-high heat.
In a bowl, combine the shrimp, olive oil, chili powder, garlic powder, cumin, salt, and pepper. Toss until the shrimp are well coated.
Thread the shrimp onto skewers for easier grilling, if desired. Grill the shrimp for about 2-3 minutes on each side, or until they are pink and opaque. Remove from heat.
To assemble the tostadas, place a tostada shell on a plate. Layer with shredded lettuce, grilled shrimp, a generous scoop of guacamole, and a spoonful of pico de gallo.
Squeeze fresh lime juice over the top and garnish with cilantro. Repeat with remaining tostada shells.
Serve immediately and enjoy!