Stem basil and reserve half the leaves for garnish. Stack remaining leaves, roll into a long cylinder, and slice across length to create very thin strips (chiffonade). Cut tomatoes into 1/4" dice. Trim cucumber, peel, and cut into a fine dice. Mince garlic. Peel and halve onion. Slice half the onion into thin strips (julienne) and finely dice other half.

Preheat outdoor grill or grill pan to medium heat. Lightly spray grill or grill pan with cooking spray. Spread basil pesto on flatbreads. Arrange mozzarella rounds evenly on flatbreads. Top with julienned red onion.

Place flatbreads on grill and cover with lid to melt cheese. (If using a grill pan, cover pan with foil.) Cook 8-10 minutes, or until flatbread is crisped and cheese is melted and slightly browned. Remove from grill and allow to cool before serving.

While flatbreads grill, start salad. In a mixing bowl, combine garlic, tomatoes, cucumber, and diced red onion with 1 tsp. olive oil and balsamic vinegar. Toss and refrigerate. Right before serving, add feta cheese and basil chiffonade (reserving whole leaves for pizza garnish). Season with a pinch of salt and pepper.

Halve or quarter flatbreads and arrange on a plate. Garnish with fresh whole basil leaves. Add a serving of cucumber-tomato salad next to flatbread. Garnish with black pepper.