Add the tofu cubes to a large mixing bowl together with grated ginger, apple cider vinegar, tamari, paprika, and celery salt. Mix together well and set aside to marinade, covered, for around 20-25 minutes at least*.
In the meantime, prepare the vegetables. Chop the potatoes into bite-sized pieces, and thinly slice the mushrooms and onions.
Add the potatoes, mushrooms, onions and garlic to a large mixing bowl and then add the tofu, pouring over the marinade. Stir together really well.
Transfer the tofu and vegetables to a large baking tray covered with baking paper, and season to taste with black pepper. Roast in the preheated oven for 40-45 minutes, until the potatoes are fork-tender and the tofu is crispy.
Serve immediately, or store in the fridge for 3-4 days in an airtight container.
For best results, leave to marinade in the fridge overnight, covered.