In small skillet saute' butter,onions,serrano pepper and garlic. Let cool.
In large bowl, combine tuna chunks,cilantro,celery,walnuts,sauteed onions/garlic/serrano peppers,bread crumbs,old bay,salt and coarse pepper.
Fold in mayonnasie and mustard.
Fill up tomato cups. Grate your favorite cheese on top
Cook on BBQ with rack covered with foil 10-12 minutes medium heat or in oven at 325 degrees for 10 min. or skillet med.heat 10 min.
Serve with romaine salad and garlic bread drizzle your favorite dressing on top of tuna cup and salad, I like a creamy avocado vinaigrette