For the honey mustard: Whisk together the mustard, honey and vinegar in a medium mixing bowl.
For the relish: In a medium bowl, whisk together the crema and Sriracha. Gently stir in the avocado with a rubber spatula.
For the slaw: Place the carrots, parsley, dill and cabbage in a large mixing bowl. In a small bowl, whisk together the mayonnaise, buttermilk, lemon juice, mustard and onion powder. Season with salt and pepper, and then add the dressing to the cabbage mixture. Toss to coat.
For the hot dogs: Preheat a grill over medium heat.
Halve the hot dogs lengthwise, making sure to not slice all the way through. Place the hot dogs cut-side down and grill until browned and slightly charred, about 4 minutes per side.
Brush the melted butter on the inside of the buns. Grill the buns buttered-side down until lightly browned, 2 to 3 minutes.
Place the hot dogs in the toasted buns and serve with the honey mustard, relish and slaw.