In a small bowl, combine the celery, garlic, red pepper flakes, cumin, apple cider vinegar, sugar and 2 tablespoons of olive oil. Season with 1 teaspoon of sea salt and a few turns of black pepper. Toss to combine and leave to marinate for 30–60 minutes at room temperature or overnight in the fridge.
To make the pickled golden raisins, combine all the ingredients in a small bowl. Toss to combine and set aside to pickle for 30 minutes.
Place the vegetable stock or water, 2 tablespoons of olive oil and ½ teaspoon of sea salt in a saucepan and bring to a boil. Remove from the heat and add the couscous to the pan. Stir, then cover and let stand for 5 minutes. Fluff the couscous with a fork and set aside.
In a large serving bowl, place the couscous, marinated celery and all the pickling liquid, the pickled golden raisins (drain off the raisin pickling liquid but keep it in case the salad needs more acidity), feta (if using) and herbs and toss to combine. Drizzle with 2–3 tablespoons of olive oil, season with sea salt and black pepper and toss again. Taste and, if it needs more acid, add 1–2 tablespoons of the raisin pickling liquid. Top with the almonds and serve at room temperature.