1 tablespoon grainy mustard
2 teaspoons white-wine vinegar
Coarse salt and ground pepper
1/4 sweet onion (such as Vidalia), thinly sliced
1 Kirby cucumber, cut into thin strips
1 tomato, halved, seeded, and thinly sliced
1/2 cup celery leaves
2 tablespoons chopped sport pepper or peperoncini
4 beef hot dogs
4 hot dog buns, grilled
4 pickle spears
In a medium bowl, whisk together grainy mustard and white-wine vinegar; season with coarse salt and ground pepper. Add sweet onion, cucumber, tomato, celery leaves, and sport pepper; toss to combine.
Grill hot dogs over medium-high heat until charred and heated through, 6 to 8 minutes. Serve hot dogs in grilled hot dog buns and top each with a pickle spear and relish.