If making the glaze: Pour the balsamic vinegar into a small saucepan. Bring to a simmer over medium heat. Reduce heat to low and cook gently, stirring occasionally, until the vinegar has reduced by about half and coats the back of a spoon (about 10-15 minutes). Remove from heat and let cool; it will thicken further as it cools.

Prepare the watermelon slices. Ensure each piece is roughly 1 inch thick and cut into manageable serving-sized squares or rounds. Pat the watermelon pieces lightly with a paper towel to remove excess moisture.

Prepare the goat cheese. Slice the cold goat cheese log into rounds approximately 1/4 inch thick. If the cheese is too soft, chill it for 15 minutes before slicing.

Assemble the appetizers. Place one slice of watermelon on a serving platter. Top immediately with one slice of goat cheese.

Garnish each assembled bite generously with a sprinkle of the thinly sliced fresh mint leaves.

Finish the appetizers just before serving by lightly drizzling the cooled balsamic glaze over the cheese layer. Sprinkle with flaky sea salt and black pepper to taste.