Wash all produce thoroughly under cold running water. Pat the greens dry with a clean kitchen towel or use a salad spinner.
Slice cherry tomatoes in half, dice the cucumber into bite-sized pieces, and thinly slice the bell pepper and red onion. For a less pungent onion flavor, soak sliced red onions in ice water for 10 minutes before adding to your salad.
In a small bowl, whisk together olive oil, lemon juice, honey, minced garlic, and Dijon mustard until emulsified. Season with salt and black pepper to taste. Add your choice of fresh herbs if using.
In a large bowl, gently toss the mixed greens with half the dressing. Layer on the prepared vegetables and avocado.
Drizzle the remaining dressing over the top. Sprinkle with feta cheese and toasted nuts just before serving.