Add beef to a large Ziploc bag or baking dish and toss in balsamic vinegar, soy sauce, garlic powder, herbs, salt and pepper, olive oil and brown sugar. Let marinate 20 minutes at room temperature.
Heat a large skillet over medium-high heat; cook and stir beef until browned, 3 to 4 minutes. Set aside.
n a small bowl whisk together olive oil, orange and lemon juice. Season with salt and pepper.
Arrange salad: In a large serving bowl, salad mix, peaches, feta, and beef. Drizzle with dressing and gently toss. Serve immediately.
