Preheat oven to 350 F and line a shallow baking sheet. Using a sharp knife or metal skewer, poke holes all over spaghetti squash. Place whole squash on shallow baking sheet and bake for 1 hour and 15 minutes, turning squash halfway through baking time.
Remove squash from oven and let cool for 15 minutes. Preheat oven to 400 F for baking later. Oil or grease a 2.5 quart casserole dish.
While Squash is cooling, combine in a medium to large sauce pan over medium low heat: ricotta cheese, heavy cream, parmesan cheese, lemon juice, lemon zest, garlic powder, sea salt, and black pepper. Whisk together and warm until ricotta is melted and creamy.
Add chopped cooked chicken and stir. Turn off heat.
Cut spaghetti squash in half. scoop out any seeds. Scrape out noodles with a large spoon and add the 3 cups squash noodles to the sauce pan. Stir together to combine.
Place all the noodle and sauce mixture into the prepared casserole dish. Spread around evenly in dish. Sprinkle with chopped tomatoes if desired. Bake for 15 to 20 minutes. Remove from oven and garnish with optional parsley. Serve.
*all nutritional data are estimates based on the products I used*