Place the zest and juice of the oranges and lemon in a nonreactive Dutch oven such as Le Creuset. Peel, quarter, and core the apples and pears and toss them in the juice. Add the brown sugar, butter, and cinnamon and cover the pot. Bake for 1 1/4 to 1 1/2 hours, until the apples and pears are tender. Mix with a whisk until the applesauce is smooth but still a little chunky. Depending on the ripeness of the fruit, the apples will likely fall apart and the pears will break up and stay chunky. Serve warm or at room temperature.