To make pico de gallo: In bowl, mix tomatoes, onion, cilantro, jalapeno, lime juice and salt. Cover and refrigerate until ready to use.
To make guacamole: In bowl, mix avocados, lime juice, 1/4 cup pico de gallo, garlic, olive oil, jalapeno and salt. Cover and refrigerate until ready to use.
To make shrimp tostadas: In bowl, combine shrimp, olive oil, chili powder, cumin and salt. Marinate in refrigerator at least 15 minutes or up to 2 hours.
Preheat grill to medium-high heat. Clean and season grill grates. Grill shrimp 2-3 minutes per side until lightly charred and opaque.
Heat refried beans and spread 2 tablespoons beans on each tostada flat.
Spread shredded romaine lettuce on top of beans followed by guacamole and remaining pico de gallo.
Top each tostada with 3-4 grilled shrimp and sprinkle with Cotija cheese. Garnish each tostada with one cilantro sprig and one lime wedge.