Preheat your oven to 350°F (175°C). Slice the grapefruit in half and use a sharp paring knife to loosen the segments around the inside edges. Place the halves cut-side-up on a baking sheet or baking dish.

In a small mixing bowl, combine the oats, oat flour, chopped walnuts, cinnamon, and salt.

Pour in the melted butter (or coconut oil) and honey, then stir until the mixture is crumbly and moistened.

Evenly divide the oatmeal crumble mixture over the grapefruit halves, pressing it down slightly so it sits on top of the fruit.

Bake for 15–20 minutes until the crumble topping is golden brown and crispy. For extra crispiness, you can broil it for the last 2-3 minutes.

Let it cool for a few minutes, then top with a dollop of Greek yogurt and an extra drizzle of honey if desired.