1.  Rinse the shrimp, then drain on a paper-towel-lined plate and pat dry. Season lightly with salt and pepper.

2. In a large frying pan over medium-high heat, warm 1 tablespoon oil until hot but not smoking. Working in batches if needed, add the shrimp and cook, turning once, until firm and cooked through, 1 to 2 minutes per side for regular shrimp, 2 to 3 minutes per side for jumbo shrimp. Transfer to a plate. Add more oil between batches if needed. 
While the shrimp cook, start the salad. 
 

3.  Make the dressing and salad

• Peel the shallots and cut them crosswise into thin slices. Separate the slices into rings.
• Zest the lime and juice half, keeping the zest and juice separate. Cut half into wedges for garnish. (Zest and juice 1 lime; cut 1 lime into wedges.)
• Trim the ends from the mango; cut away the peel, then cut the flesh away from the pit into halves. Thinly slice the halves crosswise.
• Strip the mint leaves from the stems.

In a small bowl, stir together the shallots, fish sauce, garlic, coconut sugar, lime zest, 1 tablespoon (2 TBL) lime juice, and 2 tablespoons (¼ cup) water. 

4.  In a large bowl, toss together the arugula, shellfish, mango, mint, walnuts, and 1 tablespoon (2 TBL) dressing (set aside the remaining dressing for serving). Season to taste with salt and pepper.

5. Transfer the salad to individual plates and serve the lime wedges and remaining dressing on the side.