In a large salad bowl, combine the mixed salad greens, cherry tomatoes, cucumber, bell pepper, radishes, red onion, avocado, and feta cheese.
In a small bowl or jar, whisk together the olive oil, lemon juice, Dijon mustard, honey, salt, and pepper until well combined.
Drizzle the lemon vinaigrette over the salad and toss gently to combine.
If using, sprinkle the chopped walnuts on top for added crunch.
Serve immediately or chill in the refrigerator for up to 30 minutes before serving for a refreshing taste.