Place frozen turkey burgers on lightly oiled, preheated grill/griddle. Cook 4 to 6 minutes per side, flipping at least twice. Cook to an internal temperature of 165 degrees F.
Meanwhile, heat oil in a nonstick skillet. Add mushrooms and lightly sauté mushrooms until they are soft and glisten.
Place 1-ounce slice Swiss cheese atop each hot burger and allow cheese to melt. Add 1 tablespoon scallions and 2 tablespoons cooked mushrooms.
Spread 1 teaspoon mustard on bottom half of each roll.
Place burgers on rolls and top with 1 tablespoon sour cream.
Serve lettuce and tomato on side as garnish or on turkey burger.