Wash and spin the baby spinach under cool, running water, then dry.
Hull and slice strawberries; thinly slice red onion.
In a small bowl, whisk together balsamic vinegar, olive oil, honey, salt, and pepper.
In a large salad bowl, combine spinach, strawberries, red onion, walnuts, and feta; drizzle with dressing and toss gently.
Serve immediately or refrigerate without dressing until ready to serve.
