Preheat the oven to 375 °F.
Cut spaghetti squash in half and scoop out seeds. Drizzle with olive oil, sea salt, and black pepper.
Line baking sheet with parchment paper.
Lay spaghetti squash face down on baking sheet, and add 1/4 cup water. Bake for about 30 minutes until fork tender. Let cool.
Once cool, scrape out spaghetti squash using a fork and place in a medium mixing bowl and set aside.
In a small skillet over medium-heat, heat oil and sauté garlic. Add spinach and sauté until wilted.
Add spinach and garlic mixture, shredded chicken, tomato sauce, egg and spices to the bowl with the spaghetti squash. Mix until well combined.
Transfer entire mixture to a baking dish.
Sprinkle with red pepper flakes if desired.
Bake at 375 °F for 12 minutes. If you want a crusty top, broil for 3 or 4 minutes.