Cut each banana in half crosswise, and cut each piece in half lengthwise. Set banana pieces aside.
Bring water to a boil in a large nonstick skillet. Add the coffee granules, brown sugar, and margarine; reduce heat to medium, and cook until sugar dissolves, stirring frequently. Add banana pieces; cook 5 minutes, turning occasionally. Remove from heat, and stir in Kahlúa. Spoon over frozen yogurt.
