3/4 cup mayonnaise
1 tablespoon fresh lemon juice
1 teaspoon Cajun or Creole seasoning blend
1/4 teaspoon hot pepper sauce
1/2 pound andouille sausage, cut into scant 1/4-inch cubes
3/4 cup pecans, toasted, chopped
1 teaspoon salt
1/4 teaspoon ground black pepper
1 1/2 pounds ground beef chuck or ground beef (20 percent fat)
1 1/2 pounds onions, thinly sliced
2 tablespoons olive oil plus more for brushing grill rack
3 garlic cloves, minced
1 tablespoon golden brown sugar
6 large hamburger buns, split
8 ounces crumbled blue cheese
12 pickled okra pods, halved lengthwise*
3 cups watercress tops
For mayonnaise: Mix all ingredients in small bowl. Cover and chill.
Do ahead: Can be made 2 days ahead. Keep chilled.
For burgers: Toss first 4 ingredients in large bowl. Add beef; blend gently. Shape mixture into six 1/2-inch-thick patties. Transfer patties to small baking sheet.
Do ahead: Can be made 1 day ahead. Cover and chill.
For onions: Prepare barbecue (medium-high heat). Toss onions and next 3 ingredients in large skillet. Place skillet on grill; cook until onions are golden, stirring often, about 25 minutes. Remove from grill; season with salt and pepper.
Brush grill rack with olive oil. Grill buns, cut side down, until golden, about 2 minutes. Transfer buns to work surface. Grill burgers until brown on bottom, about 3 minutes. Turn over; sprinkle with cheese. Grill until burgers are cooked to desired doneness, about 3 minutes for medium. Place some onions, then burger, on each bun bottom. Top each with okra and watercress. Spread mayonnaise on cut side of bun tops; place on burgers. Serve with remaining mayonnaise.
*Look for pickled okra where the pickles and relishes are displayed.