There are far more varieties of radishes than just those small red ones that come to mind. Here we opted for Watermelon, which are larger and milder than regular radishes.
Preheat oven to 400°F. Line a 15x10-inch pan with foil; lightly oil foil. Toss radishes and fennel with 2 teaspoons olive oil, 1/4 teaspoon salt, and 1/4 teaspoon black pepper. Spread at one end of prepared pan. Roast 15 minutes.
Meanwhile, season salmon with 1/4 teaspoon salt and 1/4 teaspoon black pepper. Arrange skin side down at other end of pan. Drizzle 1 teaspoon olive oil over salmon. Roast 10 to 15 minutes more or until fish flakes easily when tested with a fork and radishes and fennel are fork-tender.
For vinaigrette: In a screw-top jar combine 3 tablespoons olive oil, the orange zest and juice, vinegar, and honey. Cover; shake well to combine. Season to taste with salt and pepper. Drizzle vinaigrette over salmon and vegetables. Top with orange slices and fennel fronds. Serves 4.