In a small bowl, whisk together 2 tablespoons olive oil, 1 teaspoon salt, 1/2 teaspoon pepper, garlic powder, and dried thyme. Rub mixture all over chicken breasts, coating both sides. Let sit at room temperature for 15 minutes.
Heat grill pan or outdoor grill over medium-high heat. Cook chicken for 6-7 minutes per side until internal temperature reaches 165°F. Remove from heat and let rest for 5 minutes before slicing into strips.
While chicken rests, prepare mixed greens in a large bowl. Top with sliced strawberries, red onion, feta cheese, and candied walnuts.
For the dressing, combine remaining strawberries, balsamic vinegar, honey, and Dijon mustard in a blender. Blend until smooth, then slowly drizzle in 1/3 cup olive oil while blending. Season with salt and pepper to taste.
Slice rested chicken into strips. Arrange over prepared salad. Drizzle with strawberry balsamic dressing just before serving. Toss gently and enjoy immediately.