In a large bowl, combine the fresh spinach, sliced strawberries, blueberries, and thinly sliced red onion.
In a small bowl or jar, whisk together the olive oil, apple cider vinegar, honey, poppy seeds, salt, and pepper until well combined. This is your poppy seed dressing.
Pour about half of the dressing over the salad ingredients and toss gently to coat.
Sprinkle the crumbled feta cheese and toasted pecans over the salad.
Drizzle with additional dressing if desired, and serve immediately.
Notes
This salad is best enjoyed fresh. You can customize it with other berries or nuts of your choice. For a heartier meal, add grilled chicken or shrimp.