I am a big believer that a sandwich can be a beautiful thing, when you start with great quality ingredients. You will love this one as a great lunch or dinner served with a fresh salad on the side. You can also try it in a tortilla or without the bread completely, for a less filling option.
Combine all ingredients in a small bowl and stir until blended. Cover with plastic wrap and store in fridge until ready to use. Leftover mayonnaise can be stored in the fridge for up to one week.
Rub tuna with sesame oil and sprinkle with sesame and coriander seeds. Season with salt tuna and pepper.
Heat vegetable oil in a large hot skillet over medium high setting. Sear tuna for 1-2 minutes per side, until it starts turning white but still pink in the middle. Do not fully cook or it will be dry. Remove immediately and begin preparing sandwiches.
Assemble sandwich to your liking layering, mayo, seared tuna, avocado, tomato and lettuce leaves. Serve immediately with your favourite salad.