Prepare Chicken Cassoulet: Lightly coat an unheated 4-quart nonstick saucepan or Dutch oven with cooking spray. Preheat over medium-high heat. Add chicken thighs to hot pan and cook until browned on both sides. Remove from pan; set aside.
Add oil to pan. Add leeks and sweet pepper. Cook for 5 minutes or until tender, stirring occasionally. If desired, carefully add wine. Bring to boiling and cook until wine is nearly evaporated. Stir in beans, broth, thyme, salt and black pepper. Bring to boiling; reduce heat. Place chicken thighs on top of bean mixture. Simmer, covered, for 20 minutes or until chicken thighs are no longer pink (180°F).
Meanwhile, prepare Gremolata: In a small bowl, combine parsley, lemon peel and garlic. Set aside.
To serve, divide beans and chicken among six shallow serving bowls. Sprinkle with Gremolata just before serving.