Preheat the oven to 400°
Cut the squash in half and remove the seeds and membrane with a spoon. Drizzle and coat the inside with olive oil and season liberally with salt and pepper. Place skin side up on a baking sheet and bake for 35-40 min (depending on weight) or until visibly tender. Remove from oven and allow to cool.
While the squash is baking, dice chicken into ½ cubes. Season with italian seasoning, onion powder, salt and pepper and place in a hot skillet over medium high heat.
Cook for about 5 minutes or until no longer pink. Add in garlic and stir. Cook for 1-2 minutes or until fragrant. Deglaze the pan with chicken stock, allowing to come to a simmer until reduced by half.
Add half and half and ⅓ cup of parmesan cheese. Simmer until thickened enough to coat a spoon.
Add in lemon zest and fresh broccoli and cook for another 2-3 minutes or until the broccoli turns bright green and is just shy of tender.
If using frozen broccoli, steam in microwave according to package directions (if not already defrosted)drain excess water, and set aside. Adding frozen directly into sauce will will cause the sauce to be too thin/watery.
With oven mitts on (as the squash will be hot), carefully use a fork to pull the "spaghetti" out of the squash halves, leaving a thin layer of the flesh in the skin to keep the skin stable enough to act as a bowl. Place spaghetti in a large bowl.
To the bowl, add alfredo sauce with chicken and broccoli (or add defrosted, drained broccoli directly) to the bowl. Add in raw, peeled shrimp. DO NOT cook shrimp in the sauce on the stove, as it will become overcooked and tough.
Reduce oven temperature to 350°.
Top stuffed spaghetti squash with mozzarella and remaining parmesan cheese. Bake for an additional 20 minutes. For the last 5 minutes, turn on the broiler to brown the cheese (optional).
Top with chopped parsley and serve immediately.