Tartar Sauce:
In small bowl, combine the mayonnaise, olive oil, red onion, dill, chilies and capers. Whisk the ingredients together and season with salt and pepper.
Cover and chill. (Sauce can be made 2 days ahead.)
Burgers:
1. Prepare barbecue (medium heat).
Form ground turkey into four 1/2 inch-thick patties. Sprinkle with salt and pepper.
Grill burgers until cooked through, about 5 minutes per side.
Grill buns until just toasted.
Spread 1 tablespoon sauce on bottom half of each bun. Top each with 1 burger, then 1 more tablespoon sauce. Top each with 1 onion slice, 2 tomato slices, then the lettuce. Cover with bun tops.
Serve, passing remaining tartar sauce separately.
Chipotle give these burgers a terrific kick. Adding sliced tomatoes, grilled onions and some crispy lettuce and you have a meal on a bun.