Add raw cashews, firm tofu, ¼ cup water, lemon juice, distilled white vinegar, nutritional yeast, salt, garlic powder, onion powder, dijon mustard, soy sauce, miso paste and turmeric to the blender or food processor and blend until smooth. It will be thick. Leave it in the blender, and set aside.
Prepare an 8x4 loaf pan by spraying it with non-stick spray. Set aside.
Add 1 cup of water to a saucepan along with agar agar powder and bring to the boil, stirring constantly.
When it comes to a rolling boil, set a timer for 1 minute and let it boil, while you continue to stir, for the full 1 minute.
Moving very quickly, as the agar agar begins to set fast, pour the agar agar mix into the blender on top of the other blended ingredients and blend it in quickly.
Immediately pour this out into your prepared 8x4 loaf pan. Smooth it down and then place it into the fridge to set. It starts to set very quickly but should be completely set and firm within an hour.
Once set, loosen the sides with a knife and then tip it out onto a wooden cutting board. Cut into slices. Don't make the slices too thin or they will be too fragile for the grill pan. You want them fairly thick.
Place the slices onto a parchment lined baking sheet and brush them with olive oil.
Heat a non stick grill pan over medium heat. When the pan is hot, place the halloumi strips into the pan and let them sear and cook for about 2 minutes until browned with grill lines. Then flip them over and cook the other side for about 2 minutes until browned with grill lines.
Repeat with the next batch of vegan halloumi slices. Serve warm.