In a 9x13-inch baking dish, pour the sliced peaches along with their syrup. Spread them evenly across the bottom.
In a small bowl, mix together the cinnamon and brown sugar. Sprinkle this mixture over the peaches for added flavor.
Evenly spread the dry yellow cake mix over the peaches. Do not stir; let it sit as the cake mix will absorb the moisture from the peaches while baking.
Drizzle the melted butter over the dry cake mix, ensuring it's covered well.
If using, sprinkle the chopped pecans over the top for an extra crunch.
Bake in the preheated oven for 45-50 minutes, or until the top is golden brown and the edges are bubbling.
Remove from the oven and allow to cool slightly before serving.
Notes
Serve warm with vanilla ice cream for an extra treat.