Season chicken on both sides with salt and pepper. Brush chicken on both sides with some of the balsamic dressing.Cook chicken on the stove in a greased skillet or on the grill over medium heat for 5-7 minutes on each side until cooked through. Brush again with balsamic dressing on both sides and cook another 1-2 minutes. Transfer to a plate or cutting board and slice into strips.Assemble salads with spinach leaves on the bottom. Top with strawberries, apples, chicken, feta cheese, and pecans.Serve salad immediately with remaining balsamic dressing.