Preheat oven to 400 F. Melt butter, peel and dice apples and shred zucchini over paper towels (then fold over and gently press down to remove most of moisture).
Whisk together eggs, sugar, milk. Then add melted butter. In another bowl mix flour, baking powder and salt.
Slowly incorporate flour mixture into egg mix. Fold in zucchini and apples now. If you wanted to add some finely chopped nuts inside you could do that now too.
Spoon into muffin pan that have muffin liners or have been sprayed with non stick spray. Fill 3/4 of the way full.
If adding topping mix those ingredients in a bowl and sprinkle on top.
Bake for approx. 17-20 minutes or until top springs back when gently touched in the middle, or a toothpick comes out mostly clean with crumbs on it.