1. Heat oil in a skillet over medium heat. Add onions and sauté until soft. Add frozen spinach and spices, to taste. Cook for two to three minutes. Remove from heat.
2. Drain the excess liquid. In a large bowl, combine spinach mixture with defrosted gefilte fish.
3. Spread gefilte fish mixture over salmon. Roll salmon jelly roll style. Freeze overnight.
4. Remove salmon roll from freezer and let thaw slightly. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Grease a baking sheet. Cut salmon roll into half inch slices and place on prepared baking sheet. Bake for 25 minutes.
Serve with dill dip: 1 cup mayonnaise, 4 cubes frozen dill, 1 tablespoon lemon juice, 1 clove garlic (crushed), salt and pepper to taste. Blend.