1. In an 8-inch baking dish, mix salmon with lemon juice and arrange in a single layer.
2. Tightly cover dish with foil. Bake in a 450° oven until fish is opaque but still moist-looking in thickest part (cut to test), 12 to 14 minutes.
3. Meanwhile, in a blender or food processor, smoothly purée red peppers, parmesan, cornstarch, chili, and garlic. Add cilantro and broth; whirl to blend.
4. Pour pepper mixture into a 10- to 12-inch frying pan. Stir over high heat until boiling; keep warm.
5. Meanwhile, cook pasta in 3 quarts boiling water until tender to bite, about 7 minutes. Drain; return to pan.
6. Stir juices from the baked salmon into red pepper sauce. Mix 1 1/3 cups sauce with pasta.
7. Spoon pasta onto plates. Top with fish and drizzle with remaining sauce. Serve, or cover and chill up to 1 day.