Stir in peanut butter and chili powder and the gradually add the coconut milk, stirring constantly, to form a thick sauce. If too thick, add a little water, but the sauce should be thick enough to not run when spread on the nori.
To make the filling, mix tamari through cooked brown rice. Lay each nori sheet on a board and, with a pastry brush, lightly brush nori with lemon juice.
Over three quarters of nori sheet, spread a thin, even layer of peanut sauce.
Lay brown rice evenly on top and, in centre of sheet, lay 2 slices of avocado in a line.
Roll nori sheet up to firm a cylinder.
Cover nori with plastic wrap and rest for at least 30 minutes before serving.
To serve, cut each nori i to 3 equal-sized mini-rolls with a very sharp knife and arrange decoratively on a Japanese dish.