Preheat oven to 350 degrees. Grease and flour a 9x13 pan.
In a small bowl, mix the mashed banana with the lemon juice and honey and set aside. In a medium bowl, whisk together the flour, baking soda, baking powder, salt, and nutmeg.
In a large bowl, cream together the butter and sugar until fluffy. Beat in the eggs one at a time, and add the vanilla. In a bowl or large measuring cup, stir together the buttermilk and yogurt.
Gently fold in the flour mixture alternately with the milk/yogurt mixture, starting and ending with the flour. Fold in the banana mixture.
Pour into prepared pan and bake until a toothpick comes out clean, 45 to 55 minutes. Let cool completely. Beat cream cheese, powdered sugar, vanilla, and milk together to make a smooth frosting. Spread on top of the cake and sprinkle with chopped toasted pecans.