Preheat the oven to 350 degrees Fahrenheit. Spray a 9x13 pan and set aside.
In a large bowl, combine the 2 cans of peaches in heavy syrup and the other drained peaches.
Pour the 1/4 cup brown sugar, 1 tbsp cornstarch, 1 tsp cinnamon, 2 tsp vanilla, lemon juice of 1/2 lemon and 1/2 tsp salt over the peaches. Mix to combine.
Pour the peaches into the prepared pan.
In a medium-sized bowl add the boxed cake mix, 8 tbsp melted butter, and 1/4 cup brown sugar. Combine until a crumble forms.
Pour this crumble over the top of the peaches.
Bake in the oven for 40-50 minutes until the filling is bubbling and the crumble is browned.
Remove from the oven and allow it to cool for 10-15 minutes. Serve warm with ice cream. Enjoy!