To make the dressing, whisk together orange juice, lime juice, zest, pepper, salt and sugar in a small bowl. Set aside.

To make the salad, thaw shrimp and drain off any excess liquid. 

In a medium bowl, combine shrimp with mint, cilantro, cheese, cucumber and tomatoes. 

Halve avocados and discard pits.

With a table knife, gently score flesh of avocado without splitting the shell. 

Scoop out avocado and add to shrimp salad, reserving avocado shells. 

Pour half of the dressing over the salad and gently toss to coat. 

In another bowl, toss romaine with remaining dressing. 

To serve, divide lettuce among plates. 

Set avocado shells on greens and fill with shrimp salad. 

Garnish with additional cheese, mint and cilantro leaves and serve.