Preheat oven to 300°F. Line a large rimmed baking sheet with parchment paper.
Fill a large bowl half-full with water. Add 2 cups pumpkin seeds to the water; swish with your hands to remove any excess pumpkin flesh, which should sink to the bottom of the bowl. Use a slotted spoon to remove the seeds from the bowl; pat them dry with a paper towel.
Spread the pumpkin seeds in an even layer on the prepared baking sheet. Bake, stirring once, until starting to brown, about 40 minutes.
Meanwhile, mix 1 large egg white, 1 teaspoon salt and seasoning (if using) in a medium bowl.
Carefully add the pumpkin seeds to the egg white mixture. Stir well to combine. Spread the seeds in a single layer on the baking sheet. Bake until light brown, about 15 minutes more. Let cool for 10 minutes before serving.
