Preheat oven to 375F. Line 1 large baking sheet (or 2 small) with parchment paper. In bowl, combine tuna, mayonnaise, celery, garlic, 2 tbsp sliced chives, dill, Dijon, hot pepper sauce, lemon zest, salt and pepper. Mix to combine. Divide tuna mixture onto toast slices and arrange onto prepared baking sheets, leaving lots of space between. Top each slice with cheddar. Sprinkle small border of cheese around edges of each toast. Bake at until cheese on edges is crisped and lacy, about 10 minutes. Let stand on pan for 5 minutes before serving. Top with extra sliced chives.