Add the chicken stock to the onion and green pepper and simmer over moderate heat for 5 minutes. Add the tomatillos, tomato, garlic, cayenne and the roasted red peppers and simmer over moderate heat for 10 minutes. Season the sauce with salt and pepper and pour into 2 large baking dishes. Set the chicken legs on top of the sauce, skin side up. Bake for about 25 minutes, or until the chicken is deeply browned and cooked through. Scatter the scallions and cilantro over the chicken and serve.