In a large nonstick skillet, melt butter. Add olive oil, onions and salt. Cover and cook over low heat about 20 minutes and then uncover and turn heat to medium. Stir frequently and cook until onions are brown and caramelized – about 5 minutes. In the meantime, cook pasta according to package directions. Drain and keep warm.
Preheat the oven’s broiler to 500 degrees F, with top rack set approximately 6 inches from the heat source.
Line a cookie sheet or jelly roll pan with foil or lightly spray with non-stick cooking spray. Place salmon filets skin-side down on pan and broil on top rack approximately 3 minutes. Turn salmon fillets over and broil for approximately 3 additional minutes, until it flakes easily with fork; then break into large bite-sized pieces.
Stir together onions, pepper, dill, and parsley. Combine with pasta and salmon; sprinkle Parmesan cheese over top and serve immediately.