WHISK 2 tbsp oil with vinegar and 1/8 tsp each salt and pepper in a large bowl. Set aside.
SPRINKLE turkey with remaining 1/8 tsp salt and pepper. Heat remaining 1 tbsp oil in a large non-stick frying pan over medium-high. Add 4 pieces of turkey and cook until just golden, 1 to 2 min per side. Remove to a platter and cover with foil to keep warm. Repeat with remaining turkey, adding more oil, if needed.
ADD capers, garlic and lemon slices to pan. Cook for 30 sec. Add broth and reduce heat to medium. Gently boil until reduced to 1/2 cup, about 5 min. Stir in lemon zest and butter. Return scallopini to sauce and warm through, 30 sec. Add mesclun to dressing, toss and serve with turkey.