To make the filling, put the walnuts and almonds into a high-speed blender or food processor and pulse until broken up. Add the rest of the filling ingredients and pulse until the tomatoes are well incorporated and the mixture is meaty-looking. Tweak the flavours to taste (you may want more liquid aminos and salt) and set aside.
To make the pico de gallo, combine all the ingredients in a bowl. Add more coriander, garlic, chilli, lime juice, onion or salt, to taste.
To assemble the tacos, scoop about 1 tbs of filling into the groove of a lettuce leaf. Add a spoonful of pico de gallo, a couple of avocado slices, and a drizzle of sour cream. Repeat with the remaining leaves.