Grease an 8-inch springform pan with coconut oil or prepare a 10-inch square baking pan with oil and drape with parchment paper.
Whisk the flour, baking powder, salt, sugar and orange zest. Set aside.
In a separate bowl whisk the coconut oil, applesauce, milk and rosewater. NOTE: If everything is cold the coconut oil may clump. Work with room temp. wet ingredients. Whisk until everything is evenly combined.
Pour the liquid mixture into the flour mixture, stirring until just combined. Do not over-mix.
Pour into the baking pan. Top with roasted rhubarb, followed by crump topping.
Bake on the center rack for 45 minutes to one hour, until golden brown and the center has set when a tooth pick is inserted and comes out clean. If baking in a 10-inch square pan bake for 30-35 minutes.
Recipe by phoebe's pure food at https://www.phoebespurefood.com/rhubarb-crumb-cake/