1. Drizzle the tuna with lemon on both sides and sprinkle with salt.
2. Mix all the spices together in a bowl. Dip each cut side of the fillets into the spice mixture, so as to cover the surface well.
3. Heat the broiler, the charcoal grill or a griddle, and grill the tuna fillets until seared and firm. Be careful not to overcook.
4. Serve immediately with lemon wedges and drizzle with fresh olive oil, if you like.