Preheat oven to 350°.
Place sweet potatoes in a large pot of water and boil until tender, about 10 minutes. Drain well and mash or purée until smooth and creamy. Add orange juice and zest, spices, 2 pinches salt, vanilla, ½ cup maple syrup, and dissolved arrowroot. Mix well and set aside.
In a large bowl, combine oat flour, whole-wheat pastry flour, and 1 pinch salt. In a separate bowl, whisk together 3 tablespoons maple syrup, oil, and water. Add wet ingredients to dry and stir until well combined. With moistened fingertips, pat oat mixture into an oiled 8-inch pie plate. Bake for 10 minutes.
Pour sweet potato filling into baked crust. Leave enough room for pecan topping. Set aside.
Scatter pecans on a baking sheet and bake at 350° for 8–10 minutes, or until toasted. Combine barley malt and remaining 1 tablespoon maple syrup; toss with pecans until shiny but not drenched. Drain pecans. Arrange pecans on top of pie filling. Bake about 40 minutes, or until pecan topping is bubbling and caramelized and crust edges are brown. Cool before serving.