Preheat oven to 350 degrees F. Liberally grease a 13x9" baking pan with cooking spray; fill the bottom of the pan with the halved donut holes until they're tightly packed in the pan in an even layer.
Mix together the melted butter, brown sugar, cinnamon, nutmeg, beaten eggs and vanilla with a whisk until blended; pour the mixture evenly over top of the donut hole pieces, smoothing it over the top if needed so all the pieces are coated. Set aside.
In a medium bowl, combine the crumble ingredients until thick, coarse crumbs are formed. Crumble the streusel mixture over top of the bars as evenly as possible. Bake for approx. 18-22 minutes or until the top is golden and the center appears set and not super jiggly. Cool completely in the pan before cutting into squares.
*NOTE: the bars aren't as solid as say, a brownie. They tend to fall apart as they're dense. You probably won't get super clean cuts from this but you may if it sets longer, such as overnight. Note that this is almost like a casserole bake rather than a definitive bar.