1. Peel and clean the shrimp. Using a small, sharp knife, butterfly the shrimp open by slicing almost all the way through the back side. This will help the shrimp lay more flat while marinating and cooking.
2. Rinse the shrimp in cold water and pat dry with paper towels and transfer back to shallow glass dish.
3. Add the juice of the 8 key limes, making sure the shrimp is covered with lime juice. Cover and chill while you prep the rest of ingredients.
4. To the blender, add the red Fresno peppers, habaneros, juice of 4 key limes, grapeseed oil and salt to taste. Pulse or blend until desired consistency. Taste for salt.
5. Pour this mixture over the shrimp/lime mixture making sure it’s mixed in evenly. Season with fresh cracked pepper.
6. Layer the cucumbers, onions, and cilantro over the top. Chill for just 15 more minutes. The shrimp will be ready to eat after only 30 minutes. Before serving, mix all together. Serve with tostadas.