• Peel the shallots and thinly slice them crosswise. Separate the slices into rings.

In a small bowl, stir together the shallots, nuoc cham base, and 2 tablespoons [¼ cup] water.

For the shrimp or jumbo shrimp:

• Rinse and drain the shrimp. Pat dry on a paper-towel-lined plate. Season lightly with salt and pepper.

In a large frying pan over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. 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.

For the scallops:

• Pat the scallops dry with a paper towel; season lightly with salt.

In a large frying pan over high heat, warm 2 to 3 teaspoons oil until hot but not smoking. Add the scallops and cook without turning until golden brown on one side and starting to turn opaque, 2 to 4 minutes. Turn and continue cooking for about 30 seconds for translucent or 1 to 2 minutes for opaque. Transfer to a plate.

While the shellfish cooks, start preparing the remaining ingredients.

• Trim the root end from the romaine heart; thinly slice the leaves.
• 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.
• Trim the root ends from the scallions; thinly slice the scallions.

In a large bowl, toss together the romaine, mango, scallions, carrots, walnuts, shellfish, and 1 tablespoon [2 TBL] dressing (set aside the remaining dressing for serving). Season to taste with salt and pepper.

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