Prep your watermelon, cucumber, mint, and basil, and add them to a salad bowl. Add the feta as well (I'd start with 1/2 cup and add more if needed).
You can either add the vinegar and oil to a jar and shake it up or just drizzle a bit on top of the salad and toss like I did. I didn't put quantities because everyone's tastes vary, but I would start with 1-2 teaspoons balsamic vinegar and a tablespoon of olive oil and go from there.
Season with salt & pepper as needed (feta is pretty salty so you may be able to skip the salt) and serve immediately.
Notes
I encourage you to play with ingredient quantities in this salad to suit your tastes.
One mini watermelon weighs around 5-7 pounds typically... you can definitely cut up a large watermelon and use part of it for this salad instead.
Nutritional information is provided as a courtesy only and should be construed as an estimate rather than a guarantee. Ingredients can vary and Salt & Lavender makes no guarantees to the accuracy of this information.