Preheat oven to 375°F. Combine
salmon, spinach, celery, and pasta in an ovenproof baking dish.
Heat milk in a small sauce pan;
don't let it boil. Stir in mustard and half of the Gruyere cheese until it melts.
Add
sun-dried tomatoes and fennel seeds. Let cook for a few minutes until tomatoes are
softened.
Pour sauce over the salmon mixture.
Top with remaining Gruyere cheese. Cover with aluminum foil and bake for 30 minutes.