Combine the mayonnaise and ½ the sriracha in a bowl until the mixture is an orange-pink color. Set in the refrigerator.
In a large bowl, fold together the chopped shrimp, breadcrumbs and eggs. Add the remaining sriracha, green onions, dehydrated onion, parsley, lemon zest, smoked paprika, salt, black pepper and crushed red pepper to form a smooth, slightly spicy batter.
Form the mixture into patties, pressing just hard enough that the cake holds together, and pan-fry in olive oil until golden brown on both sides.
Add more olive oil to the skillet as needed.
Serve with a dollop of the sriracha mayonnaise, garnishing each shrimp cake with a lemon wedge and green onions.