1. Preheat oven to 350°F. Grease a 9x5-inch loaf pan.
2. Combine ingredients for streusel topping in a medium bowl and combine with fingers to create a crumbly topping with the butter evenly distributed. Set aside.
3. Whisk the flour, baking soda, and baking powder in a small bowl to combine. Set aside.
4. On medium speed, beat the sugar and vegetable oil to combine. Add the eggs, one at a time, beating after each until combined. Add the mashed bananas and vanilla extract; beat to combine. Alternatively add the flour mixture and milk, beginning and ending with the flour. Beat just until the flour is incorporated and finish mixing with a spatula.
5. Spread batter into the prepared loaf pan. Sprinkle the streusel topping evenly over the batter. Bake until a thin knife inserted in the center comes out almost clean, about 60 minutes.
6. To make the rum glaze, combine the butter, water and sugar in a saucepan over medium-high heat and bring to a boil. Immediately reduce the heat to medium-low and simmer for 5 minutes. Remove from the heat and stir in the rum. Set aside and cover to keep warm.
7. Cool the cake on a wire rack for 5 minutes. Then, using a skewer poke holes all over the top of the loaf. Spoon about ¼ cup of the rum glaze all over the loaf. Let the cake sit for about 5 minutes and then spoon the remaining glaze over it, a little at a time, until it is all absorbed into the bread.