Scrub, half and seed orange and cut into 2" chunks. Peel, core, and cut apple into 2" chunks. Scrub, seed and cut lemon into 2" chunks. Combine the orange, apple, and lemon in food processor and pulse until finely chopped. Add the cranberries and pulse until the berries are coarsely chopped. Transfer to a bowl and stir in the sugar and walnuts.