Combine the tartar with the dukkah. Combine the sour cream with the lime zest, salt and pepper. Combine the lime juice, chilli and avocado and finely mash with a fork. Using a serving ring, cut out a circle from 1 slice of toast and, using the cutter, place on a plate. Spread half the tartar and half the avocado paste on the toast in layers. Remove the cutter. Repeat to create a second circle and garnish with rocket.