Preheat oven to 300°F. Lightly coat a rimmed baking sheet with nonstick spray. Lightly beat egg white in a small bowl until frothy. Add pumpkin seeds, sesame seeds, sugar, salt, cayenne, and cardamom and stir to coat.
Spread out seed mixture on prepared baking sheet and bake, stirring every 5 minutes or so, until pumpkin seeds are toasted and mixture is dry, 18–22 minutes. Let cool.
Sprinkle can be made 1 week ahead. Store airtight at room temperature.
