Poke holes in the skin of the potato with a fork and microwave for 3 minutes. Turn and cook another 3 minutes. They are done when you insert a knife and they feel soft. Allow to cool for 10 minutes. Peel the potato and mash well or pass through a potato ricer.
Add the zucchini to a towel squeeze out as much liquid as possible.
Use a 1 tablespoon measuring spoon, scoop out the mix and form into balls. They will be sticky and may not form properly, this is ok.
Refrigerate the balls for 30 minutes to help them set. Roll them again to shape.
Roll the balls in breadcrumbs to evenly coat.
Add oil to a high sided pan, fill halfway and heat until it reaches 320°F on a candy thermometer.
Fry the balls in batches depending on the size of your pan, so they are not crowded for 1-2 minutes until golden brown.
Drain onto a paper towel. Serve with marinara dipping sauce.