In a small pot, bring the vinegar, honey, salt, bay leaf and 1/2 cup water to a simmer. Turn off the heat, transfer to a medium bowl and stir in the fennel. Let come to room temperature, about 15 to 20 minutes.
Heat a grill or grill pan over medium heat. Grill the summer sausage until crisp, 5 minutes. Flip the sausage, and make stacks of 3 to 4 slices on the grill. Top each stack with a couple of pieces of cheese, cover the grill and let cook until melted. Remove from the heat and drain on paper towels.
Spread the slider buns with butter and grill until lightly toasted. Place some pickled fennel on the bottom piece of a slider bun. Top with a stack of the cheese-grilled summer sausage, a crisp piece of lettuce and a dollop of Sriracha Lime Mayo. Repeat with the remaining ingredients. The sweet and sour balance takes it to another level.
Sriracha Lime Mayo:
Yield:About 1 1/4 cups
Mix together the mayonnaise, Sriracha, honey and lime juice in a small bowl.