Preheat oven to 425°F. Line a large baking sheet with parchment paper or coat with oil.
Cut the spaghetti squash in half lengthwise and scoop the seeds and stringy bits out with a spoon and discard. Place the squash cut-side-up on a baking sheet and drizzle with olive oil. Bake in preheated oven for 25 minutes.
1 large spaghetti squash, Olive oil
Remove squash from the oven and add the chicken breast and broccoli. Drizzle chicken and broccoli with olive oil and salt and pepper. Bake for another 15-18, or until the internal temperature of teh chicken reaches 165.
1 lb chicken breasts, 1/2 lb broccoli florets, Salt and pepper to taste
While the chicken and squash cook, make the sauce. Melt the butter in a saucepan over medium heat. Cook the garlic for 2-3 minutes. Add the flour and stir to create a thick paste (roux). Whisk constantly while you pour in the 2 cups of milk. Continue to stir until it's thick and no lumps remain. Add up to 1 cup more milk to thin the sauce as needed. Stir in the parmesan cheese until it melts. Taste and add salt and pepper as needed.
2 Tablespoons butter, 4 cloves garlic, 2 Tablespoons flour, 2-3 cups whole milk, 1/4 cup parmesan cheese, ¼ teaspoon Salt and pepper to taste
Remove the sheet pan from the oven and allow it to cool slightly, until the squash is cool enough to handle. Shred the squash with a fork then divide the broccoli between each. Divide the alfredo sauce evenly, leaving some to top the boats. Mix to combine the shredded squash, broccoli, and sauce.
Cut the chicken into slices or chunks and place it on top of each zucchini boat. Pour the remaining alfredo sauce on top and sprinkle with parmesan cheese.
Place back in the oven for 15 minutes until cheese bubbles and turns golden brown. Serve with chopped parsley or fresh basil.