In a fry pan, sauté chopped onions with a drizzle of olive oil over medium heat for a few minutes until golden. Then add rest of sauce ingredients (except the arrowroot flour) and stir. Bring the sauce to a boil, then reduce to a simmer and cook for 3-5 minutes. Sprinkle arrowroot flour into sauce and whisk until sauce thickens (do not over cook, because the sauce will become too thick), then remove from heat.
Add cooked spaghetti squash and tuna to sauce, combine, and serve!
