Start by whisking together olive oil, lime juice, maple syrup, chopped mint, salt, and pepper in a small bowl. I like to taste it here and adjust sweetness or acidity before adding to the salad.
In a large bowl, add arugula, blackberries, blueberries, diced avocado, cucumber, feta, and hazelnuts. I make sure everything is evenly distributed so each bite has a mix of flavors.
Pour the vinaigrette over the salad and gently toss to coat everything. Be careful not to mash the avocado. I usually serve it immediately for the freshest taste.