Season both sides of salmon with salt and pepper, set aside.
Chop baby spinach.
In a large pan, saute onion in olive oil until soft and translucent.
Add spinach to the pan, cook until it’s wilted and the resulting water has cooked off. Remove from heat.
Mix together Ricotta, Feta, dill, lemon zest , green onion slices, and garlic powder. Add spinach, season with salt and pepper, to taste.
Once you’re happy with the flavour, mix in the egg until well combined.
Spread mixture over the salmon.
Starting from one of the short sides, roll salmon tightly, going up the length of it.
Wrap in parchment paper, or the butcher type paper the fish came in, if applicable. Place in freezer for 1 hour, to firm up a little - this will make it easier to cut.
Preheat oven to 400 F, line a baking sheet with parchment paper, set aside.
Unwrap salmon roll, slice into 6 servings, and secure end of each with a toothpick. Arrange on prepared baking sheet.
Cook for 18-20 minutes, until cooked through.
Serve hot.