Cook pasta according to package directions, omitting salt and fat. Drain. Keep warm.
Melt butter in a large nonstick skillet over medium-high heat. Add onion; sauté 4 minutes or until tender. Add broth and cheese; cook 4 minutes or until cheese melts, stirring frequently. Add tomato, peas, and salmon; cook 3 minutes or until thoroughly heated. Stir in dill, salt, and pepper.
Combine pasta and salmon mixture in a large bowl; toss gently.