Finely chop the onion and add to a saute pan. Continue to prepare the celery, then the leek, garlic, and red pepper, adding to the pan once ready. Continue to saute in garlic oil until just starting to turn golden.
Thoroughly wash and rinse the quinoa in a fine sieve, then add to the pan along with about 500ml vegetable stock. Cover with a lid and simmer for 20 minutes, stirring occasionally. Add the remaining 100ml water if it starts to stick.
The quinoa is cooked when the grains have turned translucent and become tender. When it's nearly ready, dry-fry the sliced halloumi until golden and bubbling (a couple of minutes for the first side and a further minute for the second side).