Preheat oven to 400°F. Trim the ends off the zucchini and cut them in half lengthwise. Use a spoon to carefully scrape out all of the seeds in the center, forming a boat for the filling.
Drizzle zucchini with olive oil, rubbing it both on the skin and cut sides. Place cut side up on a baking sheet. Sprinkle with salt and pepper to taste. Bake for 10 minutes. Set aside until filling is made.
While zucchini cooks, place 1 tbsp of butter in a pan over medium-high heat. Once melted, add diced onion and garlic to the pan, sauteing 4-5 minutes or until just barely softened. Add frozen spinach, stirring to combine with onion and garlic. Saute for 1-2 minutes or until spinach is no longer frozen. Season with salt and pepper to taste.
Add alfredo sauce to the pan stirring frequently to prevent burning. Add 1/2 cup of parmesan cheese, ricotta, remaining Italian seasoning, and pepper stirring well until smooth. Stir in shredded chicken until filling is well mixed.
In a small bowl, melt remaining butter. Once melted, add panko and 2 tbsp parmesan and stir until well mixed and panko is coated with butter.
Fill the zucchini boats with the chicken mixture. Top each boat with mozzarella followed by the crumb topping. Bake for an additional 8 minutes, then switch the oven to broil and broil for 2 minutes, or until crumb topping and mozzarella is golden brown. Serve immediately while hot.