If using rolls, tear bread into segments of 2 or 3 rolls depending on the length of your hot dog. Slice bread rolls ⅔'s through to create a divot for the hot dog. Lightly brush bread with melted butter. Place in broiler for a couple seconds or let toast on the grill.
Preheat grill to medium-high heat. Place hot dogs on grill. Cook for about 5 minutes on each side, or until heated through.
While the hot dogs are heating up, prepare toppings.
To make pesto mayo, combine mayonnaise and basil pesto in a small bowl. Stir until pesto is evenly distributed. Transfer to a squeeze bottle for easy serving.
To serve, place heated hot dog on toasted bread bun. Place sliced avocado on one side of the hot dog. Place arugula on the other side. Add sliced tomatoes on top of hot dog. Drizzle pesto mayo over all the ingredients. Over the mayo, sprinkle fried onions. Enjoy immediately.