Remove skins from the tomatillos, rinse them, then add all ingredients into a blender and blitz until smooth. Season with salt to taste.
To prepare the tostadas, shallow fry the corn tortillas in hot oil, over a medium high heat, until golden brown and crisp. Lift them of out the oil, place onto some paper towel to absorb any excess oil then sprinkle them with a pinch of salt.
Dice the tuna into small cubes, then mix in a bowl with the remaining ingredients for the sauce.
To serve, layer some salsa on each tostada, add a portion of spicy tuna on top then garnish with toasted sesame seeds, coriander, thinly julienned white onion and a squeeze of lime juice. Serve with an ice cold beer and enjoy!