In a jar with a tightly fitting lid, add all ingredients and shake vigorously to combine. Any leftovers can be kept in the fridge for 3-5 days.
Candied Pistachios
Line a baking sheet or plate with parchment paper and set aside.
In a medium nonstick skillet or saucepan, combine the sugar, water, and (optional) salt or flavoring. Stir in the pistachios and place over medium heat. Stir continuously as the sugar melts. The mixture will first become syrupy, then start to thicken.
As the moisture evaporates, the sugar will crystallize and coat the nuts. Keep stirring gently. After a minute or two, the sugar will begin to melt again and form a glossy caramel. Watch closely to avoid burning.
Once evenly coated and golden, quickly transfer the pistachios to the parchment-lined surface. Spread them out with a spatula or fork to prevent clumping. Let cool completely (about 10–15 minutes). When completely cool, break apart.
Assemble Salad
Create a bed of the spring mix on a large platter or bowl. Arrange peaches, blackberries, red onion, and avocados. Pour the vinaigrette over salad and toss. Sprinkle crumbled cheese over salad.