To brine the shrimp, mix the water, salt, and sugar together in a sealable plastic bag until the salt and sugar dissolve. Add the (thawed, if previously frozen) shrimp and let sit in the refrigerator for 15-20 minutes. Meanwhile, line a sheet pan with foil, and place it in your broiler. Preheat the broiler with the pan inside.
When the shrimp have finished brining, rinse them, dry them with paper towels, and toss them in enough olive oil to coat. Sprinkle very lightly seasoning salt, if desired. Place the shrimp on the pan in a single layer and broil just until pink, flipping once -- about one minute per side. Remove from the pan and chill completely before serving. Serve on a bed of ice.
For the cocktail sauce:
1 14 oz can diced tomatoes
juice of 1/2 lemon
1 tbsp olive oil
1/2 tbsp sugar
chili sauce, such as Sriracha, to taste
wasabi (horseradish) powder, to taste
kosher salt and black pepper, to taste
Note: this will make more cocktail sauce than you need, but you can save a portion for a few days in the refrigerator or up to 2 weeks in the freezer. Sriracha chili sauce is usually available in the Asian/ethnic foods section of the grocery store.
Drain the tomatoes and pour into a blender or food processor along with the lemon juice, olive oil, and sugar. Blend to a thick puree. Add the rest of the ingredients to taste, mixing well. Refrigerate to chill before serving.