For the burger: Peel away the outer layers of each lettuce head to get a diameter of 5 to 6 inches. On opposite sides, slice two 1-inch slices from the sides of the head to form the top and bottom of the bun. Repeat with the remaining heads. Set the slices aside. Refrigerate the remainder of the lettuce for another use.
Mix the bison, jalapeno, Gruyere, salt and pepper in a medium bowl. Divide into 4 patties, about 8-ounces each. Flatten each patty so that it's flat and thin, about 4 1/2 to 5 inches in diameter and about 1 inch thick.
Preheat a skillet or cast-iron pan over high heat. Add the olive oil, swirling to coat the pan. When the olive oil begins to shimmer, add the bison burgers and cook until browned on the first side, about 3 minutes; flip and cook for 3 minutes more for medium doneness. (Note: Bison cooks faster and is leaner than beef; cooking it to medium keeps it moist and tender.) Let rest for 4 to 5 minutes.
For the yogurt ranch dressing: Combine the yogurt, buttermilk, chives, vinegar, hot sauce, parsley, dill, garlic powder, onion powder, pepper and salt in a medium bowl. Whisk until smooth.
To assemble: Take one half (the flattest half) of the iceberg slices and use it for the bottom buns. Slather each with 2 teaspoons mayonnaise and top with a bison burger, a slice of tomato, a slice of onion, and 2 bread-and-butter pickles. Follow that with a dollop (1 tablespoon) of the yogurt ranch dressing and then the tops of the lettuce bun. Secure with skewers and serve immediately.