Preheat the oven to 425 degrees.

Slice 2 lemons into 1/4 inch thick slices, discarding the seeds, and place them in a small saucepan. Cut the remaining two lemons in half and squeeze the juice into the saucepan with the lemon slices.

Add the water and salt to the saucepan. Bring the mixture to a boil over high heat, stirring until the salt dissolves. Cover and simmer over low heat for 10 minutes.

Drain the lemons then chop them finely.

Place the cauliflower on a rimmed baking sheet. Toss with the oil, coriander, cumin, and black pepper. Roast for 20 minutes, stirring once, until the cauliflower has started to brown.

Remove from the oven and mix with half of the lemon mixture. Serve sprinkled with parsley if desired.