Put one tablespoon of the oil into a large deep-sided frying or sauté pan and set over a high heat. As soon as the oil shimmers, add the halloumi and fry, tossing frequently, for a few minutes until the cheese is deeply browned.
Tip the halloumi into a bowl lined with kitchen paper, and return the pan to the heat, along with the remaining oil and the onion.
Fry the onion, again tossing the pan very frequently or the onion will burn, until lightly charred and somewhat softened about four minutes.Add the garlic and spices to the pan and fry, tossing, for a minute, then throw in the cherry tomatoes and water.
Cover the pan and allow the tomatoes to bubble and break down, just until they only vaguely retain their rounded shape – about five minutes. Stir the pan frequently so nothing catches on the bottom.
Reduce the heat to medium, and stir the halloumi into the curry, which should be much drier by now. Add the spinach (usually in one or two batches, allowing each to wilt before adding the next).
Once the spinach has wilted, remove from the heat, taste and season as required. Serve immediately.