Preheat oven to 450°.
Place flour in a medium bowl. Gradually add milk and broth, stirring with a whisk until blended.
Melt margarine in a medium saucepan over medium heat; stir in chicken broth mixture. Cook 8 minutes or until thick and bubbly, stirring constantly with a whisk. Add 1/4 cup cheese; cook 1 minute. (Cheese will not completely melt.) Remove from heat; stir in sherry.
Slice each toasted bread slice in half diagonally. Arrange 4 toast triangles on a baking sheet, overlapping triangles. Top each with 3 ounces turkey, about 3/4 cup cheese sauce, 2 tomato slices, 2 teaspoons bacon bits, and 1 tablespoon remaining cheese. Repeat procedure with remaining ingredients to make 4 sandwiches. Bake at 450° in the upper third of the oven for 8 minutes or until thoroughly heated. Sprinkle with pepper.