Cajun Spiced Burgers

Name: Cajun Spiced Burgers
Ingredients: 1 1/2 pounds 80% lean ground beef; 2 teaspoons Cajun seasoning; 3 scallions, sliced (white and green parts); 1/2 cup mayonnaise; 2 teaspoons Dijon mustard; 1 teaspoon hot sauce; 1/4 cup loosely packed fresh flat-leaf parsley leaves, chopped; 1 celery stalk, finely chopped (about 1/2 cup); 1 medium yellow onion, sliced into 1/4-inch rounds; 1 medium green bell pepper, sliced into 1/4-inch rings; 1 tablespoon vegetable oil; 4 sesame seed hamburger buns, split