Heat oven to 400°F (200°C).

Place sweet potatoes in a baking pan. Sprinkle with salt and drizzle with oil. Cover and bake for 30 minutes; uncover and bake an additional 10 minutes, or until soft when pierced with a fork.

Place the sweet potatoes in a large mixing bowl and mash with a potato masher until smooth.

Meanwhile, in a large frying pan, sauté all four onion varieties until golden. (You can use just regular and purple onion if you don’t use leek and scallions on Pesach.)

Add onion mixture to mixing bowl, along with ground and chopped nuts, salt, and pepper, and mix until thoroughly combined.

Place side of salmon on a large surface and trim to create an even, thin side of fish. (You will need to slice off some of the higher part of the salmon to achieve a flat, even shape for stuffing and rolling. You can dice the extra salmon shavings and add them into the filling mixture, or see note.)

Sprinkle salmon with kosher salt and lemon juice; allow to sit 15 minutes. Rinse salmon and pat dry.

Place stuffing mixture down center of fish, and roll over to one side so that fish will have a center full of filling when sliced.

Cut salmon to fit into two or three loaf pans and carefully place rolls into pans. Smear the top of each roll with oil and sprinkle with garlic powder and paprika.

Cover tightly and bake at 400°F (200°C) for 40 minutes. Remove cover and lower heat to 350°F (180°C) and bake an additional 15 minutes.

Slice when cold. Can be served cold or warm. Reheat covered.