Make the shrimp. Pat the shrimp dry with a paper towel to remove any excess moisture. Add to a medium bowl and toss with salt, garlic powder, onion powder, paprika, chili powder, and black pepper until evenly coated.
Melt the butter in a large skillet over medium heat. Add the seasoned shrimp and cook for 3-4 minutes, until plump and pink. Transfer to a bowl and set aside.
Make the mango pico de gallo. Add all the ingredients to a medium bowl and toss to combine. Taste and season with more salt as needed.
Assemble the tostadas. Spread about 2 tablespoons of smashed avocado on each tostada shell. Add the shrimp and top with some mango pico de gallo serve with lime wedges.
Notes
Avocado swap: Smashed black beans or a thin layer of Mexican crema both work in place of avocado.
To store: Keep the cooked shrimp and mango pico in separate containers in the fridge up to 4 days. Press plastic wrap onto leftover smashed avocado to keep it from browning. Store extra plain shells in a sealed bag in a cool, dry place.