1. With hands, tear bread slice into very small pieces. In 12-inch skillet over medium heat, heat 2 tablespoons butter or margarine (1/4 stick) and bread crumbs, stirring frequently, until crumbs are golden brown; spoon buttered crumbs into small bowl; set aside. Wipe skillet clean.
2. Spread chicken breasts open. Arrange breasts in same skillet; add lemon juice, salt, 1/2 cup water, and 2 tablespoons butter or margarine (1/4 stick); heat to boiling. Reduce heat to low; cover skillet and simmer 10 minutes. Add endive, cut side down; cover and continue cooking 5 minutes longer or until chicken and endive are fork-tender. With slotted spoon, remove chicken breasts to warm platter; top each with a piece of endive, cut side down. Sprinkle breasts and endive with capers; keep warm.
3. In cup, stir flour and 2 tablespoons water until blended. Gradually stir flour mixture into hot liquid remaining in skillet. Over medium heat, cook, stirring constantly, until mixture thickens slightly and boils. Remove skillet from heat; stir in cheese until melted. Pour cheese mixture over chicken; top with crumbs.