In a blender, combine hulled strawberries, balsamic vinegar, olive oil, salt, and ground pepper. Blend until smooth, about 30 seconds.

In a large mixing bowl, toss together the mixed greens, sliced strawberries, and crushed pecans. Drizzle half of the dressing over the salad and toss gently.

Transfer the mixed salad onto a serving platter or individual plates. Top with thinly sliced red onion and drizzle with additional dressing if desired.