Using a small food processor or immersion blender, combine mayonnaise, chili garlic sauce, sweetened condensed milk and sugar. Depending on your tastes for walking on the spicy side, add chili garlic sauce slowly until you reached your desired heat. Set aside.
Combine white and black sesame seeds in a shallow bowl or pie plate. Dredge both sides of the tuna steaks in sesame seeds. Set aside.
Heat vegetable oil in a large cast iron skillet or large frying pan over high heat.
The name of the game is to sear, which means high heat, spitting oil and in my house, the smoke detector going off, so prepare your work space accordingly.
When vegetable oil is hot, place tuna steaks in the pan, cover. Cook on each side for 2-3 minutes depending on desired temperature. Two to three minutes will be a medium rare for a 1 1/2 inch tuna steak. I like mine rare, so I go for 1-2 minutes on each side. It all depends on the thickness of your tuna steak.
Remove tuna steaks from frying pan/cast iron skillet. Plate and top with teriyaki glaze.
There are two choices for the volcano sauce. You can put a dollop on the side, allowing individuals to dip according to their tastes OR you can put the volcano sauce into an airtight plastic bag and cut a small hole on one bottom corner and then pipe the sauce onto teriyaki tuna steaks.
Garnish with scallions.
If you've tried this recipe, come back and let us know how it was!