Make the salad; in a large bowl, combine baby spinach, mint leaves (if using), strawberries, avocado, almonds, and grilled chicken.
Make the dressing; combine buttermilk, extra-virgin olive oil, and lemon juice in a bowl. Whisk until blended.
Stir in Chia seeds, and whole-grain mustard.
Add Stevia if using (adds a nice sweet balance) and salt to taste.
Serve salad and drizzle with dressing.