Pare carrots and cut in julienne strips. Dissolve bouillon cube in 1/2 cup boiling water. Add carrots and cook until tender. Meanwhile, melt margarine in skillet. Add onions and cook until soft. Remove onion. Stir in flour, salt and pepper. Add 3/4 cup water and stir until thickened. Put carrots and onions in a casserole dish and pour over sauce.