Get Organized: Set the oven at 350F. Butter a 9-inch springform pan. Dust it with flour, shaking out the excess.
Make the Rhubarb Filling: In a small bowl rub the sugar and lemon zest together with your fingers. Add the rhubarb and orange juice, toss, and set aside.
Make the Crumb Topping: In the bowl of a food processor, combine the flour, butter, brown sugar, pecans, and salt. Process until well combined. Then put the crumb topping into the refrigerator while you make the cake.
Make the Cake Batter: In a bowl, add the flour, baking powder, and salt. Whisk to combine.
With a standing mixer (or with a hand mixer), beat the butter at medium speed for 2 minutes until light and creamy. Add the sugar and beat for 2 minutes more. Beat in the vanilla. Add the eggs, one at a time, beating well after each addition. Scrape down the sides of the bowl.
With the mixer set on low, mix in the flour mixture just until the dry ingredients are blended. Add the milk and mix just until incorporated. Scrape down the bowl and give the batter a final stir with a rubber spatula.
Assemble the Cake: Spread the batter in the pan, smoothing the top with the spatula. Distribute the rhubarb over the batter and spread the crumb topping over the rhubarb.
Bake: Bake the cake for 45-50 minutes, or until a skewer inserted into the middle of the cake comes out with only a few crumbs attached.