Preheat oven to 350F. Line a 9x13 pan with foil and lightly grease.

Crust In bowl combine flour, oatmeal, brown sugar, salt, and nutmeg. Cut in butter with pastry blender until mixture resembles coarse crumbs. Measure out 1 cup and set aside. Press crust into pan and bake 8 minutes.

Filling Whisk flour, baking powder, salt, and sugar. Make a well in center and pour in butter and egg. Stir with a rubber spatula until smooth and combined. Crumble mixture over warm crust and pat into an even layer. 

In a medium bowl, toss strawberries with sugar, cornstarch, nutmeg, and vanilla. Spread evenly over filling and sprinkle reserved crust mixture over top. Bake 40-45 minutes until just lightly golden and center is no longer jiggly. Cool completely in pan. Cut into bars and serve. Store leftover bars in refrigerator.