MAKE THE CRUST: Lightly oil an 8-inch-square baking pan. Using a sharp knife, peel the orange half, removing all of the bitter white pith. Working over the bowl of a food processor, cut in between the membranes to release the sections. Squeeze the juice from the orange membranes into the bowl; discard the membranes. Add the dates and water to the processor and puree until very smooth, scraping down the side as needed, about 1 minute. Scrape the puree into a bowl. Rinse and dry the processor bowl.

In the food processor, process the almonds until very finely ground. Add the pecans, cinnamon, and ground cardamom and pulse until the pecans are coarsely chopped. Add 1/4 cup of the date puree and pulse until the mixture holds together. Using oiled fingers, press half of the nut crust into the prepared pan in an even layer. Transfer the remaining nut crust to a bowl. Rinse the processor bowl again and pat dry.

MAKE THE FILLING: Using a vegetable peeler, remove the orange zest in strips, then thinly slice the zest. Using a sharp knife, peel the orange, removing all of the bitter white pith. Working over the bowl of the processor, cut in between the membranes to release the sections. Squeeze the juice from the membranes into the bowl. Add the dates and water; puree until smooth.

Spread the filling over the crust. Crumble the nut crust evenly over the filling; press down to compact it. Refrigerate for at least 2 hours, until firm enough to cut.

Cut the bars into 18 triangles, garnish with the reserved orange zest and serve.

The bars can be refrigerated for up to 3 days