Mix warm milk with yeast and sugar. Let it sit for 5 minutes until foamy.
Add melted butter, eggs, salt, and mashed banana. Stir well, then gradually add flour. Knead the dough for 10 minutes.
Place dough in a greased bowl, cover, and let it rise for 1 hour.
Mix filling ingredients. Roll out the dough into a rectangle, spread filling, and sprinkle walnuts if using.
Roll up the dough, cut into 12 rolls, and place in a greased dish. Let rise for 30 minutes. Preheat oven to 350°F.
Bake for 25-30 minutes then spread the icing over warm rolls.