Coat a large cast-iron skillet with cooking spray; place over high heat until hot.
Add scallops; cook 2 minutes on each side or until browned.
Remove scallops from skillet; set aside, and keep warm.
Coat skillet with cooking spray.
Place over medium-high heat until hot.
Add pepper strips and garlic; saute 2 minutes or until tender.
Add vinaigrette and lemon juice, deglazing skillet by scraping particles that cling to bottom. Cook 1 minute. Return scallops to skillet, and cook until thoroughly heated.
Combine lettuce and watercress in a large bowl.
Add scallop mixture to lettuce mixture; toss lightly.