Mix pumpkin seeds, olive oil, chili powder, tamari, and garlic powder in a resealable 1-gallon plastic bag. Seal bag and knead to coat the seeds with seasonings. Spread coated seeds on a baking sheet in an even layer.
Bake in preheated oven for 15 minutes, then turn the seeds over. Bake until pumpkin seeds are lightly toasted and fragrant, about 15 more minutes. Remove from oven and sprinkle lightly with salt. Cool before serving; store in an airtight container in refrigerator.