Melt butter in a large nonstick skillet over medium-high heat. Add the mushrooms; sauté 3 minutes. Add green bell pepper and onions, and sauté 2 minutes. Lightly spoon flour into a dry measuring cup; level with a knife. Stir flour into mushroom mixture; cook 1 minute, stirring constantly.
Combine milk, Chicken Stock, and sherry. Gradually add milk mixture to pan, stirring with a whisk until blended. Bring to a boil over medium heat; cook 3 minutes or until thick, stirring constantly. Add cream cheese, stirring until smooth.
Stir in chicken, red bell peppers, salt, and nutmeg; cook 1 minute. Remove from heat. Arrange 4 toast pieces on each of 4 plates; spoon 1 cup chicken mixture over toast. Sprinkle evenly with parsley.