Use a melon baller to create balls with the cantaloupe and honey dew melon (as many as you like). Stir together vanilla yogurt, honey, and cinnamon in a small bowl. In two short glasses, layer first some cantaloupe and honey dew melon balls, then some blueberries, half of the yogurt mixture, a few heaping spoonfuls of Grape Nuts, and finish with the remainder of the yogurt mixture. Top with additional blueberries and a sprinkling of Grape Nuts for garnish.