Preheat the oven to 350°F (175°C).
In a mixing bowl, combine 4 cups of fresh sliced peaches with 1 cup of granulated sugar and 1 tablespoon of lemon juice if desired.
Pour the peach mixture into the bottom of a greased 9x13 inch baking dish, spreading it evenly.
Sprinkle the dry yellow cake mix evenly over the peach mixture, ensuring every corner is covered.
Drizzle the melted 1/2 cup of unsalted butter over the top of the cake mix.
If you love a bit of crunch, sprinkle with 1 cup of chopped nuts like pecans or walnuts before baking.
Bake in the preheated oven for about 45 minutes, or until the top turns golden brown and bubbles emerge from the peaches below.
Cool for a few minutes before serving.