To make the croutons: Preheat the oven broiler on low. Line a baking sheet with parchment paper or foil. Cut the bread into cubes and place them on the baking sheet. Drizzle the cubes with olive oil, season with garlic powder, salt and pepper, and toss until thoroughly combined. Broil until golden brown and crunchy on all sides. Toss occasionally to get an even toasting. Then set aside.
Assemble the salad: place the cucumber, tomato, onion, olives, mozzarella, and pepper in a bowl.
Make the dressing: Whisk together all of the ingredients in a bowl until fully combined. Season with salt and pepper.
Combine the croutons and dressing in the bowl with the vegetables and toss well. Season with salt and pepper to taste. Refrigerate.
Preheat a grill or grill pan over medium heat.
Season both sides of the chicken well with salt and pepper and drizzle with oil. Set aside.
Once the grill is hot, grill the chicken on each side to an internal temperature of 160℉ (71℃) using a thermometer. Once cooked, set aside to rest for 3-5 minutes. Chop the chicken into bite-sized pieces.
Mix all the ingredients for the spritzer. Serve over ice if desired.
Toss the chicken with the croutons, cucumber, tomato, olives, mozzarella, and peppers. Toss with dressing.
Serve with spritzer.