Preheat oven to 350°F. Line a rimmed baking sheet with parchment paper.
Toss the seeds with butter and salt. Place on baking sheet and bake for 10-15 minutes, stirring occasionally.
Remove from the oven and toss with sugar/syrup and cinnamon (if using). Bake an additional 10-15 minutes, stirring occasionally. Watch the seeds closely as you near the end of cooking time, as they can burn easily.