For salad, use vegetable peeler to remove a large strip of peel from cucumbers; discard. Using same peeler thinly slice cucumber and celery length-wise into long thin strips; place in large bowl. Add mint and peanuts; set aside.
For prawn fritters, in a large bowl place the prawns, snow peas, 1/2 cup cilantro, onions, lime peel, 2 tablespoons of the lime juice, egg whites, rice flour, granulated sugar, and salt; stir gently to combine. Heat 2 tablespoons of the oil in a very large skillet over medium-high heat. For each fritter, place 1/2 cup of the prawn mixture into the skillet and flatten slightly, cooking 4 fritters at a time. Cook 2 to 3 minutes per side or until golden and prawns turn opaque. Turn carefully; if necessary, use spatula to reshape. Remove fritters; keep warm. Repeat with remaining oil and prawn mixture.
To serve, toss cucumber mixture with remaining lime juice and brown sugar. Divide between serving plates. Top with fritters. Pass lime wedges. Makes 6 servings.