Put all the ingredients for the chermoula in a food processor and process to a slightly unevan puree. Smear over the tuna on both sides. Place in a shallow dish then cover and leave to marinate for at least 2 hours, turning occasionally , before cooking.
Wipe a heavy frying or griddle pan with olive oil. Place over a high heat and leave to heat through for about 3 minutes. Lay the tuna in the pan and cook the steaks for about 2 minutes on each side. Serve immediately.