In a small bowl, with a vegetable peeler, cut thin slices from each cucumber half up to seed portion. Stir in onion, vinegar, 1 teaspoon oil, salt, and black pepper; refrigerate until ready to serve.
Preheat broiler to high and place oven rack 4 to 5 inches from broiler. Coat both sides of salmon with remaining oil and lemon juice and season with lemon pepper seasoning and garlic powder; broil 8 to 10 minutes.
Meanwhile, in a small bowl, mix sour cream and dill; spread evenly over salmon. Broil 3 minutes more or until topping is lightly browned, salmon is opaque throughout and internal temperature reaches 145° F. Serve over cucumber salad and garnish with lemon and dill.