To prepare relish, combine first 8 ingredients in a bowl; toss well.
To prepare scallops, heat 1 1/2 teaspoons oil in a large nonstick skillet over medium-high heat. Sprinkle scallops with 1/4 teaspoon salt and 1/4 teaspoon pepper. Add half of scallops to pan; cook 2 minutes on each side or until done. Repeat procedure with remaining oil and scallops. Arrange scallops over watercress; top with relish. Serve with lemon wedges.