Prepare the Crust: Line a 9x13-inch baking pan with parchment paper and coat lightly with cooking spray. In a food processor, pulse walnut pieces until coarsely ground. Add flour, powdered sugar, cinnamon, and salt; pulse until combined. Incorporate unsalted butter until clumps form and press mixture firmly into the bottom of the pan. Refrigerate for 30 minutes while preheating the oven to 350°F.

Bake the Crust: Place the chilled crust in the preheated oven and bake for 20-25 minutes until lightly golden brown. Cool completely in the pan on a wire rack while preparing the cranberry curd.

Make the Cranberry Curd: In a saucepan, combine cranberries and water, and bring to a boil over medium heat. Cook for about 5 minutes until cranberries burst. Strain mixture through a fine-mesh sieve to collect the purée, discarding solids. In a bowl, mix cranberry purée with sugar, eggs, lemon juice, and a pinch of salt; whisk until smooth.

Cook the Curd: Return the cranberry mixture to the saucepan and cook over medium heat, stirring constantly for 5 to 11 minutes, until thick enough to coat the back of a spoon.

Combine and Bake: Remove from heat, stir in softened butter until melted. Pour the curd over the cooled crust and spread evenly. Return to the oven and bake for an additional 10-15 minutes until set yet slightly jiggly in the center.

Cool and Slice: Cool on a wire rack for 1 hour, then refrigerate for 2 hours until chilled and firm. Lift the bars out using parchment paper and slice into 24 equal pieces. Dust with powdered sugar and garnish with candied citrus zest, if desired.