Preheat oven to 450. In large saucepan, bring chicken broth to a boil. Place the couscous in a med bowl and drizzle with broth. Cover bowl with plastic wrap and let stand for 10 min before fluffing with a fork.
In same saucepan, combine the lentils and garlic with water to cover by 1 1/2 inches. Bring to a boil, then lower heat to a simmer and cook until lentils are tender, about 20 min.; drain. Discard garlic if desired. Stir lentils into the couscous; reserve saucepan.
Meanwhile, season chicken with salt and pepper. In small bowl whisk together 2 T oil, the ginger and cinnamon. Slather chicken with seasoned oil. In large skillet heat 1 T oil over med heat. Add chicken and cook til golden, about 6-8 minute Flip chicken then transfer skillet to the oven and roast til cooked through, about 15 minute.
In reserved saucepan heat remaining oil (I would use butter, and just 1/2 T) over med heat. Add onion and cook til golden, stirrring, about 10 minute Stir into lentil mixture along with any chicken juices. Season mixture with salt and pepper and serve with chicken.