In a small saucepan, bring 2 1⁄4 cups water, quinoa and millet to a boil. Stir once, cover, and reduce heat to low. Simmer for 15 minutes, until water is absorbed and grains are soft. Fluff with a fork.
Arrange 1 oven rack in highest position and preheat broiler to high. Line a large, rimmed baking sheet with foil and mist with cooking spray. In a small bowl, whisk together garlic, lemon juice, rosemary, oil and pepper. Rub mixture onto chicken and transfer to 12 minutes, until no longer pink inside and juices run clear. Transfer to a cutting board, let cool slightly and slice thinly against the grain.
Meanwhile, prepare dressing: In a small food processor or blender, blend dressing ingredients until smooth.
Transfer grains to a large bowl. Add spinach and dressing and toss until spinach is lightly wilted and dressing is incorporated. Fold in pear and scallions. Divide among serving plates and top with chicken and cheese.
Serving Size: 1 1/2 c grain mixture, 3 oz chicken, 1/2 oz cheese