Note from Ricardo
There are three brands of pure (gluten-free) oatmeal available on the market: Château Cream Hill, Only Oats and Bob's Red Mill. If you can’t find one of those, you can also prepare the crumble with certified gluten-free quinoa flakes.
If you find the dough is too fragile after rolling out between two sheets of parchment paper, refrigerate it for a few minutes. The paper should easily peel off the dough and it will be easier to line the tart pan.