Bring vinegar and water with sugar to a boil in a small pot. Add salt and stir to dissolve the sugar and salt completely. Reduce heat to low.
Place shallots and herbs in a food processor and pulse to finely chop. Transfer to a small plastic food storage container. Pour the hot brine over top of the shallots and herbs to cover, put a lid on the container and chill until ready to serve or let marinate at room temperature until lamb is ready to serve.