Preheat your oven to 350°F (180°C). Line a 10-cup muffin tin with paper liners or lightly grease each cup to prevent sticking.

In a medium bowl, toss the chopped strawberries and rhubarb with the maple syrup until evenly coated. Set aside to let the fruit marinate slightly.

In a separate bowl, whisk together the Greek yogurt and egg until smooth and well combined.

In a large bowl, mix the all-purpose flour, rolled oats, and brown sugar. Pour in the melted butter and stir with a spoon or your fingers until the mixture resembles coarse crumbs. It should hold together loosely when pressed.

Press about half of the crumble mixture firmly into the bottom of each muffin cup to form a solid base. This prevents sogginess from the filling later on.

Spoon about 1 tablespoon of the yogurt mixture evenly over each crumb base, spreading gently but not needing to fully cover the crumbs.

Add a generous spoonful of the maple-coated fruit on top of the yogurt layer in each cup.

Sprinkle the remaining crumble mixture evenly over the fruit, lightly pressing to hold some crumbs in place but keeping that crumbly texture.

Bake in the oven for 24 to 28 minutes. Look for a golden-brown color on the topping and bubbling fruit juices. The edges should be firm while the yogurt layer sets without cracking.

Remove from the oven and allow the crumble cups to cool completely in the pan before taking them out. This helps maintain their shape and prevents falling apart.