In a large coffee mug or glass measuring cup, mix the agar powder into 2 cups water and let sit for about 30 minutes.
In a high-speed blender, blend the cashews, coconut oil, apple cider vinegar, lemon juice, nutritional yeast, onion powder, salt, and tapioca with agar and water mixture until completely smooth, about 2 minutes. Scrape down the sides of the blender with a rubber spatula to make sure you get everything.
Transfer to a saucepot. Heat over medium and cook, stirring often with a rubber spatula, until the cheese mixture is thick and glossy and pulling away from the sides of the pot, about 10 minutes.
Fill a 6-quart pot or bowl halfway with water and add about 15 ice cubes. Salt it well so it tastes like seawater.This is the brine for the mozzarella.
Use an ice cream scoop to scoop a cheese ball into the ice water. Dip the ice cream scooper all the way into the ice water to release the ball. It will firm up and start setting right away. Continue until all the mixture is used.
Cover the container, refrigerate, and let the cheese set for at least an hour. It’s ready to use!