Preheat oven to 350°. In a small bowl, stir together the cucumber, sour cream, yogurt, dill, 1 minced garlic clove, 1 tablespoon lemon juice, and salt and pepper to taste. Set aside.
Line a large baking pan with aluminum foil. Rinse salmon and pat dry; put skin side down in the pan. Sprinkle with remaining minced garlic clove, lemon juice, and salt and pepper to taste. Bake until barely opaque in the center, 10 to 15 minutes.
Serve salmon warm or cold with yogurt sauce. Garnish with dill sprigs, if you like.
Note: Nutritional analysis is per serving.