Preheat the oven broiler.
For the Watermelon Mint Drink: Mix the ingredients for the drink together and refrigerate until ready to serve.
Season the chicken well on both sides with salt and pepper and drizzle with oil.
Preheat the grill on medium heat.
Grill the chicken well on both sides to an internal temperature of 160°F (71℃) using a thermometer. Once cooked, set aside to rest for 5 minutes before dicing into bite sized pieces.
Make the dressing: In a small bowl, whisk together all the ingredients until thick and emulsified. Season with salt and pepper to taste.
Toast the bread. Spread with butter and garlic. Top with cheese. Place under the broiler until melted and bubbly.
Top the greens with berries, pistachios, red onion, goat cheese, chicken, and cucumber, then drizzle with the dressing.
Serve the salad with bread and watermelon mint juice.