Preheat your oven to 375°F (190°C). In a large mixing bowl, combine chopped rhubarb, granulated sugar, lemon juice, and all-purpose flour. Stir until well-coated.

In a separate bowl, mix all-purpose flour, granulated sugar, cinnamon, and a pinch of salt. Cut in cold butter until the mixture resembles coarse crumbs.

Pour the rhubarb filling into a pre-prepared pie crust and cover with the crumble topping.

Bake for 45-50 minutes until the filling bubbles and the topping is golden brown.

Let the pie cool for at least 30 minutes before slicing.