Spray a large nonstick skillet with canola oil spray and heat over medium-high heat. Add the bacon and cook until very lightly browned, about 3 minutes per side. Cool slightly and cut into thin strips.
Whisk together the vinegar, olive oil and salt and pepper to taste in a large bowl. Add the carrots, peas and scallions and toss. Add the watercress and toss again. Transfer to a large platter and top with the bacon.