Place blueberries and strawberries in small separate bowls. Combine vinaigrette with 1 Tbsp. chopped mint. Gently stir half the dressing into blueberries and remaining half into strawberries.
Divide blueberries among 8 cocktail glasses. Spoon about 1 Tbsp. crumbled cheese over each portion of blueberries; top with strawberries. Garnish with mint leaves if desired. Serve immediately, or cover and chill up to 30 minutes. Makes 8 servings.