Place the arugula, watermelon, feta, and mint in a large bowl.
In a small container with a lid, mix together the olive oil, lemon juice, mustard, and salt and pepper. Shake vigorously to combine.
Just before serving, drizzle the dressing over the salad mixture and toss to coat. Sprinkle on chopped hazelnuts or sunflower seeds.
Notes
I like to use chopped hazelnuts on this salad for the extra crunch and flavor. You can leave them off, or use sunflower seeds, slivered almonds, or another type of nut you like.
The salad doesn't keep for long after the dressing has been added. It will start to wilt within an hour. If you aren't sure you'll use the whole salad at once, only dress the servings you'll use, so the remaining salad can be preserved for later.
The information shown is an estimate provided by an online nutrition calculator. It should not be considered a substitute for a professional nutritionist’s advice.