Cut the spaghetti squash in half, scrape out the seeds, and place it in a rimmed baking dish face-down with 1/4 cup of water. Bake at 375 F for 1 hour, or until soft. Once cooked, set aside until cool enough to handle. Once cooled, scrape the squash out into a large bowl.
For the sauce, add all the coconut aminos to a large skillet over medium heat. Simmer for 10 to 15 minutes, or until it thickens to coat the back of a spoon. Scrape the sauce into a separate bowl and add the vinegar, sesame oil, and fish sauce. Whisk to combine and set aside.
To the skillet, add the olive oil and the onion. Saute the onion for 5 to 10 minutes, or until browned and fragrant. Add the cabbage, celery, and garlic. Saute over medium-high heat, stirring occasionally so that it develops a slight char.
Once the vegetables are cooked, stir in the spaghetti squash and the sauce. Mix to combine, garnish with the sesame seeds and onion, and serve!