Mix the rhubarb and strawberries with the tapioca and sugar. Let mixture rest at least 5 minutes.
Mix up the crumble topping ingredients. (I use my fingers)
Stir the filling mixture again, then pour into the crust.
Top with the crumb topping.
Bake at 400F for about an hour. Check periodically to see that the crust and/or topping isn’t getting too dark. If it is, loosely place a piece of aluminum foil on top.
When the filling is bubbling up vigorously on the sides, remove and cool on a rack.
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Notes
Go higher or lower on the sugar depending on whether you like things sweeter or tarter. The topping also adds sweetness.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.