In a wide, shallow bowl or glass container, whisk together soy sauce or tamari, coconut sugar, garlic powder, rice vinegar, and sesame oil. Remove about 1/3 of the marinade (~2 ½ Tbsp if making the default number of servings) and reserve for making glaze.
Add the cubed tofu to the dish with the marinade, stir (or cover with a lid and shake) to coat well, cover, and let sit at room temperature for 30 minutes to marinate.
While the tofu is marinating, whisk together the arrowroot and a splash of water in a small saucepan, then add the reserved marinade. Bring to a simmer, whisking frequently until thickened to a glossy glaze — about 2-3 minutes. If it thickens too much, add a little water to thin. If it’s too thin, whisk more arrowroot with water, then add to the saucepan and cook to thicken.
Once the tofu has finished marinating, lightly oil a grill pan or grill grate and preheat to medium-high. Thread cubed tofu and red onion onto skewers, alternating with 1 piece of red onion in between each tofu cube and ending with a piece of red onion. There should be ~8 tofu cubes per skewer.
Next, grill! Make sure as many tofu cubes as possible are making contact with the pan, and turn every 3-4 minutes, until browned and beginning to char in spots — about 10-15 minutes.
Transfer to a serving plate, brush the reserved glaze over the tofu, and sprinkle with sesame seeds and sliced green onion (both optional). These skewers are delicious served with rice and steamed broccoli or alongside our Creamy Sesame Noodle Salad.
Leftover grilled tofu keeps stored in the refrigerator for 2-3 days.
*Nutrition information is a rough estimate calculated with 1/4 tsp avocado oil for greasing grill pan and without optional ingredients.