Spread the pecans on a rimmed baking pan and bake until lightly toasted, about 4 minutes. Cool completely.
Butter a 9-by-13-inch baking pan, then line it with parchment paper, leaving a 2-inch overhang on 2 sides; butter the parchment and sides of the pan.
To make the shortbread crust: Pulse the pecans in a food processor until finely ground. Transfer to the bowl of a stand mixer fitted with the paddle attachment. Add the flour and mix on low speed to combine. Add the granulated sugar, salt and butter and mix on medium speed until the dough comes together, scraping down the sides of the bowl as needed. Remove 2 cups of the dough and reserve. Turn the remaining dough out into the prepared baking pan and press evenly into the bottom of the pan. Dock the dough all over with a fork.
Bake until light golden brown, about 20 minutes. Set on a cooling rack to cool completely, about 30 minutes. Keep the oven on.
For the filling: Put 1/4 cup of the pomegranate juice in a small bowl and stir in the cornstarch; set aside. Combine the cranberries, granulated sugar, orange zest and remaining 3/4 cup pomegranate juice in a medium saucepan. Bring to a brisk simmer over medium-high heat and simmer, lightly mashing the cranberries, until some of the liquid has reduced and the cranberries are just starting to soften, 5 to 8 minutes. Add the cornstarch mixture and simmer until thickened, 1 to 2 minutes. Pour into a bowl and submerge the bowl into a larger bowl of ice water to cool, about 10 minutes.
Pour the cooled filling over the crust and spread it evenly. Crumble the reserved dough evenly over the top, then bake until the filling is bubbling and the crumbs are golden brown, 30 to 35 minutes. Cool completely in the pan, about 30 minutes.
Dust generously with confectioners' sugar and cinnamon. Remove from the pan, trim the edges if desired and cut into squares.