In a small bowl or jar, whisk together olive oil, balsamic vinegar, maple syrup, Dijon mustard, salt, and pepper to make the dressing.
In a large salad bowl, combine arugula, blackberries, avocado slices, cucumber, red onion, and mint.
Drizzle the dressing over the salad and gently toss to combine.
Top with chopped pistachios and crumbled feta. Serve immediately.