Heat oven to 325 F. Line baking sheet with parchment paper.

In blender or mini food processor, pulse pumpkin seeds, olive oil, garlic powder, cayenne, 1/4 tsp salt, and black pepper until mixture forms a semi-dry paste. Alternatively, in bowl, finely chop pumpkin seeds and mix with other ingredients.

Coat salmon fillets with pumpkin seed mixture. Bake salmon for 18 minutes, or until just barely cooked through in the center.

As salmon cooks, place sweet potatoes in large saucepan. Cover with cold water. Bring to a boil over high heat. Boil, uncovered, for 15 minutes, or until tender. Drain and mash with butter, thyme, mustard, and 1/4 tsp salt. Alternatively, steam sweet potato cubes until tender and then mash with the other ingredients.

Spread sweet potato mash on serving plates and top with salmon.