Blend together butter, brown sugar, and cinnamon in a small bowl. Cut pear in half and remove core with a melon baller; cut off stem and blossom end. Do not peel pear.
Place each half pear, cored side up, on a large square of doubled heavy-duty foil. Scoop up half the butter-sugar mixture and form into a ball with your hands; press into cored pear cavity. Gather foil up around pear half and squeeze juice from 1 orange half over pear. Close foil around pear. Repeat with other pear half.
Place foil-wrapped pears in a preheated 350 degree oven and bake until very soft, about 1 hour. Or place on a grate over a burned-down campfire and cook until soft, moving packet often with tongs so fruit doesn't scorch, 45 minutes to 1 hour.