In a large skillet cook bacon slices until crisp. Drain on paper towels. Break in half. Wipe grease from skillet. Rinse chicken; pat dry. Add chicken broth and bay leaf to skillet. Bring to boiling. Add chicken; reduce heat. Simmer, covered, for 10 to 12 minutes or until chicken is tender and no longer pink. Drain; cool 5 minutes. Chop chicken. Discard broth and bay leaf.
In a medium saucepan heat margarine or butter and oil. Stir in flour, seasoned salt, and mustard; add milk all at once. Cook and stir over medium heat until mixture is thickened and bubbly. Cook and stir 1 minute more. Stir in cheese until melted, but do not boil. Stir in chicken; heat through.
For each serving, spoon sauce over 2 toast triangles. Serve with tomato wedges and a bacon piece. Sprinkle with sliced green onion, if desired. Makes 4 servings.