Heat the oven to 300°F (150°C) and place a rack in the middle. Line a rimmed half-sheet pan with parchment, leaving enough overhang to lift the cooled slab. Mix the oats, almonds, pumpkin seeds, sesame seeds, cinnamon, cardamom, and salt in a large bowl.
Combine the tahini, date syrup, honey, and oil in a small saucepan over low heat. Whisk for 2 to 3 minutes until fluid, then remove from heat and stir in the orange zest and vanilla.
Pour the warm binder over the dry mixture and fold for about 1 minute, scraping the bottom repeatedly until no dusty oats or dry spice pockets remain.
Spread the mixture nearly to the pan edges and press firmly into an even layer about ½ inch thick, including the corners. Bake for 25 minutes, then rotate the pan from front to back without stirring. Bake for another 18 to 23 minutes until the edges are deep gold and the center looks dry.
Set the pan on a rack and leave the slab completely untouched for 60 minutes. Do not stir, lift, or break pieces while the binder is still setting.
Lift the cooled slab by the parchment and break it into your preferred cluster size. Fold in the chopped dates and pistachios gently and transfer to an airtight container.