1. Coat a grill pan with cooking spray and heat over medium-high heat. Season chicken with the salt and black pepper; cook 8 to 10 minutes a side until cooked through. Cool 2 to 3 minutes, then slice into thin strips.
2. Meanwhile, fill a saucepan with the water and add the quinoa. Bring to a boil; reduce heat to medium low, cover and simmer 15 minutes. Fluff quinoa with a fork and then refrigerate for 30 minutes.
3. In a medium bowl, whisk together the mint, scallions, vinegar, orange juice, orange zest, mustard and oil. Mix in the walnuts, apple, red onion and cherries. Add the quinoa and toss to coat. Serve topped with chicken.