Preheat oven to 350 degrees.
Cut zucchini in half and scoop out insides. Place zucchini pulp in a bowl to reserve for later.
Drizzle about 1 T. olive oil over the insides of the zucchini and sprinkle with a little salt and pepper over each.
Place zucchini on a baking sheet, inside-up, and bake in preheated oven for 7-8 minutes.
In a medium-large sauce pan, place olive oil, onions, garlic, salt and pepper. Saute for 2-3 minutes over medium heat.
Add Italian sausage and cook over medium heat for an additional 8 minutes, or until sausage is almost done.
Measure out 1 c. of the reserved zucchini pulp. Coarsely chop and then place in the pan with the sausage. Cook over medium heat for another 2-3 minutes, or until zucchini becomes soft.
Reduce heat to a simmer and add spaghetti sauce. Once mixture is heated through, fill each zucchini boat with equal amounts of the sausage mixture. (Each boat will get about ¼ c. of the mixture.)
Top each zucchini boat with Mozzarella and 6-8 small pepperonis.
Return zucchini to the oven and broil for 2-3 minutes, watching closely so the cheese does not burn.
Top with fresh parsley and Parmesan and enjoy!