Preheat the oven to 350°F (177°C). Line a rimmed baking sheet with a sheet of parchment paper and slick it with olive oil.
In a bowl, combine the pumpkin seeds, oil, chili powder, cumin, salt, and cayenne pepper if using, and mix well.
Spread the seeds in a single layer on the baking sheet and roast for 20 to 25 minutes, stirring occasionally, until aromatic and golden brown at the edges.
☞ TESTER TIP: The seeds may start to make a popping sound after a few minutes in the oven. Don't be alarmed!
Immediately slide the sheet of parchment and the pumpkin seeds off the baking sheet to cool. Taste, and add more salt, if needed. If you have any leftover spiced pumpkin seeds, store in an airtight container.