Light and bright, sweet and savory, this pretty salad would be perfect alongside grilled meat or fish.
Whisk together vinegar, mustard, honey, shallot, salt, and pepper in a large bowl. Slowly add oil, whisking until well incorporated. Add sliced fennel bulb and radishes; toss to coat. Let stand for 5 minutes.
Add watermelon to bowl, and toss gently to coat. Use a slotted spoon to divide salad among plates. Drizzle each with some of the dressing; garnish with fennel fronds and black pepper.