Preheat the oven to 350 degrees Fahrenheit.
Add all topping ingredients to a food processor and pulse until combined. Careful not to over-process and you want to retain some texture to the walnuts.
Slice the peaches and add to a large bowl. Toss with all ingredients aside from the tapioca until well combined.
Toss in the tapioca.
Transfer to a 9 inch cast iron skillet or baking dish and spread evenly.
Add the crumble on top.
Bake for 40 minutes, then cover with foil and bake an additional 5-10 minutes. If you notice the top browning too much before the 40 minute mark, you can cover with foil earlier.
Remove from the oven and let cool, then serve with vanilla ice cream or whipped cream and enjoy!