To cook the tuna: Combine black pepper, minced almonds and sesame seeds in bowl.
Lightly salt the tuna. Mix almonds, sesame seed and pepper.
Press the tuna into mixture, until well coated. Heat sesame oil over medium-high heat. Add tuna steaks and sear about 1- 2 minutes each side (I like mine rare in the centre, longer if you prefer well-cooked tuna).
Transfer the steak to a plate and cover with aluminium foil to keep warm.
To make the Onsen Eggs: Add 4 cups of water in a heavy bottom saucepan, cover and bring it to a boil.
Once boiling, remove the pot from the heat. Take the eggs out from the refrigerator. Add 200 ml cold tap water and gently submerge the cold eggs in the hot water. Immediately cover and set timer for 17 minutes (or longer). Leave out for 5 minutes.
To make the sauce: Combine the dashi, Japanese soy sauce and mirin in a small saucepan and bring it to a boil. Add the bonito flakes and turn off the heat, let it sink to the bottom of the pan.
After 30 seconds or so, strain through the strainer and set the sauce aside.
Garnish with chopped spring onions and lemon wedges. Serve hot with the sauce.