While the grill heats, slice each croissant lengthwise but not all the way through, keeping them hinged together. Dice the onions into 1/4-inch pieces and arrange all your toppings (ketchup, mustard, relish, and diced onions) in small bowls for easy assembly. I like to prep the croissants this way so they're ready to fill the moment the hot dogs come off the grill—it keeps everything warm and fresh.

Heat your grill to medium-high heat for about 5 minutes. While it preheats, brush the frankfurters lightly with the vegetable oil and sprinkle with chili powder for extra flavor. Once the grill is hot, cook the hot dogs for about 3 minutes per side until they're nicely charred and heated through. The oil helps prevent sticking and the chili powder adds a subtle smokiness that pairs beautifully with the buttery croissant.

Lightly brush the inside of each croissant with the melted butter—this adds richness and helps toast them slightly from the residual heat of the hot dogs. Place one hot dog into each croissant, then add your desired toppings in order: mustard first (it adheres better), then relish, diced onions, and finish with ketchup. I find this order helps the flavors meld together rather than sliding around.