Preheat the oven to 400F (200C) and line a sheet pan with parchment paper. Cut the tofu into 1/2″ cubes. In a bowl large enough to hold the tofu, whisk together 2 tablespoons tamari, vinegar, and 2 tablespoons water. Toss the tofu in the vinegar mixture and set aside for 10 minutes.
Cut the spaghetti squash in half vertically. Place cut-side down on one half of the sheet pan and bake in the oven for 10 minutes. Drain marinade from tofu and add to the other half of the sheet pan. Bake another 25 minutes, tossing tofu halfway through. Squash is done when easily pierced with a fork. Remove from oven, turn squash over to let cool slightly.
While the squash and tofu are cooling, heat a few tablespoons of water over medium heat in a large skillet. Add the onion, celery, coleslaw mix, garlic and ginger, stirring to combine. Cover and cook for about 6-8 minutes, stirring occasionally, until the celery is crisp tender.
Once the spaghetti squash is cool enough to handle, carefully scoop the flesh out and add it along with the tofu to the pan with the sautéed veggies. Pour remaining 2 tablespoons tamari and sesame oil over everything and mix well. Taste, adding more tamari to adjust to taste. Heat over medium heat until mixture is warmed through. Enjoy!