- In a bowl, combine the shrimp, olive oil, chili powder, garlic powder, cumin, salt, and pepper. Toss to coat the shrimp evenly. Let marinate for 15-20 minutes. 
- Preheat the grill or a grill pan over medium-high heat. Thread the shrimp onto skewers for easy grilling. 
- Grill the shrimp for 2-3 minutes on each side until they are pink and opaque. Remove from heat. 
- In a separate bowl, prepare the pico de gallo by mixing the diced tomatoes, red onion, jalapeño, cilantro, and lime juice. Season with salt to taste. 
- To make the guacamole, combine the mashed avocado, lime juice, and a pinch of salt in a bowl. Mix until smooth. 
- To assemble, spread a layer of guacamole on each tostada shell, top with shredded lettuce, grilled shrimp, and a generous spoonful of pico de gallo. 
- Serve immediately.