To prepare the spaghetti squash, preheat oven to 400F. Line a rimmed baking sheet with parchment paper. Drizzle one teaspoon olive oil over the squash flesh and sprinkle with salt and pepper. Place cut side down on prepared pan. Bake about 45 minutes, or until the spaghetti squash strands pull apart easily with a fork. Let cool slightly before scraping all the strands into a bowl. Save the outside of the spaghetti squash if you want to serve the dish in them.
Mix all sauce ingredients in a small bowl.
In a large skillet, heat remaining teaspoon of olive oil over medium heat. Add onion and red bell pepper and cook until softened and translucent.
While the onion and red bell pepper are cooking, steam broccoli by placing it in a microwave-safe dish with 2 tablespoons of water. Cover and microwave on high for 3 - 4 minutes. Set aside.
Once onion and bell pepper and softened, add spaghetti squash, broccoli, chicken, and peanut sauce. Stir to combine and let cook for 2 - 3 minutes, until sauce has thickened and coated everything well. Season with salt and pepper.
Serve inside the spaghetti squash, if desired. Sprinkle with cilantro, chopped peanuts, and more crushed red pepper flakes.