Preheat the oven to 200C/180C Fan/Gas 6.
Mix all the salsa ingredients in a bowl with a good pinch of flaked sea salt and some black pepper and set aside.
Put the slices of bread on a board and flatten with a rolling pin until very thin. Use a plain biscuit cutter to cut out six 10cm/4in rounds and oil generously. Turn a six-hole muffin tin upside down and place on a baking tray. Brush each of the upturned holes with a little oil and press the bread rounds on top to make shallow cups. Bake for 8–10 minutes or until crisp and pale golden-brown.
Meanwhile, mix the mustard with the egg together in a small bowl. Put the oats into a jug with the almonds, sesame seeds, a good pinch of salt and some ground black pepper. Blitz with a stick blender to make a rough crumb, then shake onto a plate. Sprinkle the flour into a shallow bowl.
Dip the fish fillets, one at a time, in the flour, then the egg mixture and finally coat on all sides with the nutty oats.
Heat 2 tablespoons of the oil in a large, non-stick frying pan over a medium-high heat and fry the fish for about 3 minutes on each side, or until crisp, golden-brown and cooked through. Add a little more oil to the pan whilst cooking if needed.
Arrange the bread shells on two plates and add the shredded lettuce. Top with the salsa and fried fish pieces. Garnish with the extra coriander and serve with lemon or lime wedges for squeezing over.