Preheat the oven to 350 degrees F (175 degrees C). Grease a loaf pan with cooking spray; dust with flour.
Mash bananas in a large bowl with a fork. Add sugar and mix until smooth. Add eggs, milk, and strawberry gelatin; mix well.
Combine whole wheat flour, baking powder, and salt in a separate bowl. Add 1/2 of the flour mixture to the egg mixture; mix until moist. Add remaining flour mixture and mix until batter is just moistened.
Spread batter in the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 45 minutes.
