Toast English muffins (I do this in the oven by preheating to 350F and then toasting for 10 minutes or so, then the oven is hot to broil later.)
Mix tuna salad ingredients together (celery, dill relish, mustard, mayo, tuna, onion, and sun-dried tomato.)
Preheat oven to broil.
Spread cream cheese across the English muffins and divide tuna mixture evenly on top of them. Top each with two slices of tomatoes and ½ slice of Havarti.
Broil for 1-2 minutes until cheese is hot and bubbly. Serve immediately.