Preheat oven to 375F. Coat an 8 x 4-inch loaf pan with cooking spray; set aside.
Beat 2 T margarine and cream cheese at medium speed; add 1 cup sugar, beating well. Add egg; beat well.
Combine flour, baking powder, baking soda and salt; stir well. Combine banana, milk, rum, lime rind, lime juice and vanilla; stir well. Add flour mixture to creamed mixture alternately with banana mixture, beginning and ending with flour mixture; mix after each addition. Stir in
1/4 c pecans and 1/4 c coconut.
Pour batter into prepared pan; bake at 375F for 60 minutes. Let cool in pan 10 minutes; remove from pan. Let cool slightly on wire rack.
Topping: Combine brown sugar, margarine, lime juice and rum in saucepan; bring to a simmer. Cook 1 minute; stir constantly. Remove from heat. Stir in pecans and coconut; spoon over loaf.
Per serving: 187 cal, 5.4 g fat (26%), 2.9 g pro, 32 g carb, 1 g fiber, 15 mg chol, 105 mg sod.