In a salad bowl, combine the vinegar, honey and mustard. Add the watermelon, watercress, scallions and bell pepper and toss; season with salt and pepper.
In a large skillet, heat the oil, 2 turns of the pan, over high heat. Add the shrimp and stir-fry until pink and firm, about 3 minutes. Remove from the heat and stir in the duck sauce, soy sauce, hot sauce and lime juice; toss to coat. Serve on top of the salad.