Preheat your oven to 375°F (190°C).

In a large baking dish, combine the chopped rhubarb and strawberries, squeezing in the juice of half a lemon. Add buckwheat flour and brown sugar, stir until well-coated.

In a mixing bowl, add oats, buckwheat flour, brown sugar, and salt. Stir the dry ingredients until combined.

Add melted coconut oil to the oat mixture and mix until crumbly.

Spread the crumble topping over the fruit filling in the baking dish.

Bake for 40-45 minutes, until filling is bubbly and topping is golden brown.

Allow to cool for 10 minutes before serving with a dollop of yogurt.