Preheat oven to 350 degrees. Combine oats and sugar. Add butter, tossing to coat.
Place mixture in a shallow pan. Bake 14 to 16 minutes or until lightly toasted, stirring after 7 minutes. Let cool.
Preheat oven to 325 degrees. Line a half sheet pan with parchment.
In a food processor, process the streusel, turbinado, and half the ginger into fine crumbs.
Remove 1⁄2 cup of the mixture and reserve. To the remaining mixture in the processor add the remaining 1⁄2 tablespoon ginger, lemon zest, crystallized ginger, flour, and baking powder. Pulse until well mixed.
In a large pot, melt the honey, sorghum, and butter. Add the mixture from the processor. Stir with a wooden spoon until everything is mixed together.
Pour mixture onto a lined sheet pan. Spread evenly by pressing with hands or a spatula.
Bake for 10 minutes or longer, depending on batch size. Remove from oven and sprinkle reserved crumb mixture on hot gingerbread. Press crumbs into the layer using a spatula.