Whisk together the orange juice, lemon juice, shallots, honey, and salt. Slowly pour in the olive oil, whisking constantly, to form an emulsion. If not using within an hour, transfer the dressing to an airtight container or lidded jar and refrigerate.
Assemble the salad:
Place the arugula, watermelon, feta, and mint in a large bowl.
Drizzle with enough vinaigrette to coat the greens lightly and toss well.