Add balsamic vinegar and honey to a saucepan. Bring to a boil and immediately reduce heat to low. Let it simmer for 20 min. until sauce is reduced to about half and is a thick consistency.

Preheat a grill pan over high heat and spray the pan with cooking spray. Sear each side of the watermelon 1-2 minutes per side or until a nice char has formed.

Arrange tomatoes, mozzarella, watermelon, and basil in a large bowl. Toss gently to combine. Add the olive oil, balsamic reduction, and salt. Toss until everything is well coated.