1. Combine chicken, bread crumbs, bell pepper, walnuts, green onions, beer, parsley, lemon juice, garlic, salt and black pepper in large bowl; mix lightly. Shape chicken mixture into 4 patties.
2. Spray large skillet with cooking spray; heat over medium-high heat. Cook patties 6 to 7 minutes on each side or until cooked through (165°F). Place cheese on patties; cover skillet just until cheese melts.
3. Serve patties on buns with mustard and lettuce.