Preheat your oven to 375°F (190°C).
Get your oven ready while you mix the ingredients.
In a large bowl, toss the blueberries with the granulated sugar, cornstarch, lemon zest, and lemon juice.
This forms the fruit base.
Pour the blueberry mixture into a 10-inch skillet or a square baking dish.
Spread evenly.
For the topping, mix the flour, oats, brown sugar, cinnamon, nutmeg, and pecans in another bowl.
Add cubed butter, blending until crumbly.
Spread the topping evenly over the blueberries in your dish.
Bake until golden brown and bubbly, about 35-40 minutes.
Serve warm.