Camping Pie Iron

Camping Pie Iron

Rhubarb strawberry filling recipe help needed?

I want to make a rhubarb strawberry filling to use in a camp pie iron. I can't find a recipe online, except ones that you put in a crust and bake. I need the filling to be thickened ahead of time, as it won't be baked but for a few minutes in a fire. Should I thicken it with tapioca, flour, cornstarch, what? If you have a recipe for this type of filling, I would greatly appreciate it. Thanks!

Please look at site below.
Hope this helps.