Soak the cashews in water overnight and drain them. In a blender or food processor, combine the soaked and drained cashews, soy yogurt, lemon juice, olive oil, tapioca starch, nutritional yeast flakes, garlic powder, onion powder, and salt.

Blend the mixture for 3-5 minutes until smooth and homogeneous. Reserve the cheese mixture.

In a heavy-bottom saucepan, whisk together the soy milk and agar-agar. Bring the contents to a boil, whisking frequently. Once boiling, reduce the heat and simmer for 5 minutes, stirring almost constantly. Turn off the heat.

Transfer the mixture into an English loaf pan lined with parchment paper, smooth-out the top, and refrigerate for 12 hours, until firm.

Once set and completely chilled, remove the halloumi from the loaf pan, slice it into rectangles, and grill until golden brown.

Serve immediately. Store cheese in an air-tight container in the fridge for up to 1 week.