Prepare the balsamic glaze: In a small saucepan, combine the balsamic vinegar and honey (or maple syrup). Bring to a simmer over medium heat. Cook for 5-7 minutes, stirring occasionally, until the glaze has thickened enough to coat the back of a spoon. Remove from heat and let cool completely. It will thicken further as it cools.

In a large bowl, gently combine the cubed watermelon, crumbled feta cheese, diced cucumber, chopped mint, and thinly sliced red onion (if using). Be careful not to overmix, as this can break down the watermelon and feta.

Add about half of the cooled balsamic glaze to the watermelon mixture. Gently toss to coat. Taste and add more glaze if desired, but be mindful not to make it too wet.

Spoon the watermelon feta salad mixture evenly into 12 small cups or ramekins. Ensure each cup gets a good balance of watermelon, feta, and cucumber.

Chill the salad cups for at least 10 minutes before serving to allow the flavors to meld.

Just before serving, drizzle a little extra balsamic glaze over the top of each cup, if desired. Serve immediately.