To make the glazed walnuts, combine 1 cup brown sugar, 1 cup walnut halves, and 1/2 cup water in a small saucepan over high heat. Bring the mixture to a boil, stirring occasionally, and let it boil for about 5 minutes until the glaze thickens and coats the walnuts. Strain off any excess liquid, then spread the walnuts on a parchment-lined baking sheet to cool and harden.
In a small bowl, whisk together 1/2 cup mayonnaise, 1/4 cup heavy cream, 2 tablespoons honey, and 1 tablespoon lemon juice until smooth. Set aside.
Peel and devein 1 1/2 pounds jumbo shrimp (if needed) and remove the tails. Whisk 4 large egg whites in a medium bowl until frothy. In another bowl, stir together 1/4 cup panko breadcrumbs, 2 tablespoons cornstarch, 1 teaspoon garlic powder, 1 teaspoon salt, and 1/2 teaspoon white pepper.
Dip each shrimp in the egg whites, then coat with the breadcrumb mixture. Set the coated shrimp on a plate and prepare for frying.
Pour about 4 cups vegetable oil into a large, heavy-bottomed pot. It should be enough to cover the bottom with 2 inches of oil. Heat it to 350°F (177°C).
Working in small batches, carefully add the shrimp to the hot oil and fry for 2–3 minutes, until they are golden brown and cooked through. Remove the shrimp with a slotted spoon and drain on a paper towel-lined plate.
In a large serving bowl, toss the fried shrimp with the honey walnut sauce until evenly coated. Top with the glazed walnuts and sprinkle with sliced green onions, if desired. Serve immediately.