Preheat oven to 425 degrees. Place chicken in baking pan. Season generously with salt and pepper. Bake until cooked through, about 20 minutes. Cool completely; cut chicken into bite-size pieces.
Whisk olive oil, vinegar, mustard and sage to blend in small bowl. Combine chicken, salad greens, papaya, mango, raspberries and mint in large bowl. Add dressing and toss well. Divide mixture among 4 plates. Sprinkle with walnuts and serve.