Prepare the Salad: In a large bowl, combine the baby greens, blueberries, strawberries, cucumber, avocado, walnuts, pumpkin seeds, red onion, and feta cheese (if using). Gently toss to mix the ingredients.
Make the Dressing: In a small bowl, whisk together the olive oil, apple cider vinegar, honey or maple syrup, Dijon mustard, and a pinch of salt and pepper until well combined.
Dress the Salad: Drizzle the dressing over the salad and toss gently to ensure all the ingredients are evenly coated.
Serve: Transfer the salad to individual plates or a large serving bowl. Enjoy immediately for the best taste and texture.