Place cucumber in small colander set over small bowl; sprinkle with 1/4 teaspoon salt. Drain 1 hour.
For tzatziki sauce, stir yogurt, cucumber, 1 tablespoon lemon juice, 1/2 teaspoon lemon peel, 1/2 teaspoon garlic and 1/4 teaspoon salt in small bowl. Cover and refrigerate until ready to serve.
Combine remaining 1 tablespoon lemon juice, 1/2 teaspoon lemon peel, 1/2 teaspoon garlic, 1/4 teaspoon salt and pepper in small bowl; mix well. Rub evenly all over salmon.
Heat nonstick grill pan over medium-high heat. Cook salmon 5 minutes per side or until fish begins to flake when tested with fork. Serve tzatziki sauce.