Andouille and Beef Burgers with Spicy Mayo and Caramelized Onions

INGREDIENTS

• 3/4 cup mayonnaise
• 1 teaspoon Cajun or Creole seasoning blend
• 1 tablespoon fresh lemon juice
• 1/2 pound andouille sausage, cut into scant 1/4-inch cubes
• 6 large hamburger buns, split
• 8 ounces crumbled blue cheese
• 3/4 cup pecans, toasted, chopped
• 1/4 teaspoon hot pepper sauce
• 1 tablespoon golden brown sugar
• 3 cups watercress tops
• 3 garlic cloves, minced
• 2 tablespoons olive oil plus more for brushing grill rack
• 1 teaspoon salt
• 12 pickled okra pods, halved lengthwise*
• 1 1/2 pounds onions, thinly sliced
• 1 1/2 pounds ground beef chuck or ground beef (20 percent fat)
• 1/4 teaspoon ground black pepper