1. Heat a nonstick skillet over medium heat. Coat pan with cooking spray. Add peach and plum slices to pan; cook 3 minutes on each side or until browned.
2. Combine jam, vinegar, oil, and salt; stir with a whisk until smooth. Combine 1/4 cup jam mixture, salad greens, and romaine in a large bowl; toss well to coat. Place 2 cups greens mixture on each of 4 plates. Arrange 4 peach slices, 4 plum slices, and about 1/3 cup cucumber on each serving. Drizzle remaining vinaigrette evenly over salads; sprinkle with pepper, if desired. Serve immediately.