Rinse the tuna steaks and pat dry with paper towels.
In a small bowl, combine cumin, paprika, tumeric, anise, ginger, cinnamon, pepper flakes, salt, pepper, and lemon juice. Lightly rub both sides of the tuna steaks with 1 tbsp olive oil. Rub the seasoning mix on both sides of tuna steaks; coating them well.
Using a heavy bottomed saute pan or a cast-iron pan, warm the remaining olive oil. Increase the heat to high and place the tuna in the pan. Sear for 1 minute, then turn over carefully, reducing the heat to medium. Sear the other side for 1 more minute until medium rare. DO NOT OVERCOOK!
Pour the melted butter over the tuna steaks and sprinkle with the coriander.
(Also can do cook these on the grill -- just cook a few minutes on each side.).