Whiz one muffin top in a food processor to make crumbs. Remove.
Place the salmon in the processor and pulse until roughly chopped. Mix the salmon in a bowl with the capers, parsley, Tabasco, mustard, sea salt and pepper and egg white. Mix in 2 to 3 tbsp of the breadcrumbs. Form into four flat, large patties. Refrigerate for 30 minutes to help them set. Grill four muffin bases and keep warm. Shave the cucumber into ribbons with a veggie peeler. Heat the oil in a frying pan.
Sear the burgers on one side until crusty, turn once and cook to your liking. In the meantime, mix the ingredients for the tartare sauce together. Place cucumber on a grilled muffin half. Top with the salmon burger and a dollop of tartare, then tomato, then avocado. Serve with a lemon wedge.