Wash the pumpkins seeds thoroughly, removing all the slime from them. Dry the seeds, with a paper towel or by letting them air dry. If you are not using fresh seeds, right from the pumpkin, you can bypass this step.
Toss the seeds with the oil and Cajun spice until evenly coated. Spread the seeds evenly on a baking sheet.
Roast the pumpkin seeds in an oven at 325 for 30 minutes.