Try mixing with a hefty amount of chopped shallots (the finer the tuna the finer the shallots should be chopped), black cracked pepper, and a good quality EVOO. Let sit in fridge for a couple hours. Mix some wasabi paste with some mayo and mirin. Mix a bit in the tuna, plate the tuna (a little goes a long way - it's just an appy), put a thumb print in the top, place a bit of caviar in thumb print, drizzle with more of the mayo/wasabi mixture. Use a little less wasabi than mayo and a little more mirin than wasabi - I'm talking tsp. and tablespoons here, like 2 tsp. to 3 TBS to 4 tsp wasabi, mayo, mirin respectively.
You can also give your tuna a bit of an Asian flair by mixing in some canned water chestnuts, spring onion, toasted sesame oil, fresh grated ginger, soy sauce, bind with an egg white and when you sauté, flip ONE time only. A bit of crushed pineapple is good too! If you want some heat you can mix in wasabi or some garlic/chili paste. Serve on a bed of greens with something like a wasabi vinaigrette.