Heat 2 tablespoons oil in heavy large frying pan over medium-high heat. Sprinkle shrimp with salt and pepper; add shrimp to pan and sauté until just opaque, about 3 minutes. Transfer to plate. Mix the next 5 ingredients in large bowl. Add 5 tablespoons oil whilst mixing; season with salt and pepper. Mix in shrimp and accumulated juices, capers and green onions. Cool slightly, then cover and refrigerate at least 3 hours and up to 1 day.
Garnish with lemon rounds and fresh dill sprigs, if desired.