Preheat oven to 450 degrees. Line a baking sheet with foil and spray with Pam. Spread cut sweet potatoes out on tray and spray with Pam. Sprinkle with thyme, salt, pepper, paprika and cayenne. Bake until golden and tender, about 35-45 minutes.
Meanwhile, char eggplant over an open flame, rotating often to cook evenly, about 25 minutes. Skin should be completely black and flesh should be cooked through; place in a bowl and cover tightly with plastic to steam off skin. After about 5-10 minutes, remove charred skin leaving behind the flesh. Chop eggplant, mix with 1/2 of the yogurt and season with salt and pepper.
Preheat a grill over high heat. Split buns in half and spray split surface lightly with pam. Season burger patties lightly with salt and pepper. Add buns and burgers to grill. Allow buns to char slightly and remove. Cook burgers about 3 minutes per side for rare.
Meanwhile, in a small bowl, combine remaining yogurt with ketchup, mustard and chopped pickles. To serve spread bottom bun with some of the eggplant mixture. Place burger on top and spoon 1/4 of ketchup mixture on top of beef. Top with tomatoes, onion and lettuce and bun top. Repeat with remaining burgers and serve with sweet potato french fries.
Source: Rocco DiSpirito