Chop the onion and celery.
Heat half of the oil the oil and gently sauté the onion and celery for 5 minutes, then add the capers and cook for another minute.
Add the tomatoes, then scatter the herbs on top. Drizzle with half of the balsamic vinegar.
Put a lid on and sauté for another 5 minutes or so, until the tomatoes are tender and start bursting.
Place the salmon fillets on top. Season with salt & pepper, then drizzle the fish with the remaining oil and balsamic. Sprinkle the black cumin seeds on top.
Put the lid on and steam for 5-8 minutes over low heat.
Scatter the rocket leaves on two or four plates then put the tomatoes and salmon steaks on top. Drizzle with the jus.
Serve with chopped parsley.