Combine fennel, sunchokes, and radishes in large bowl.
Peel two oranges by running a knife all around the orange to remove the entire rind all the way down to flesh. Hold each peeled orange in your hand and run the knife on either side of each segment in a V-shape to remove each segment from its surrounding bitter membrane. Cut the resulting orange segments in half and add to salad. Scrape any excess orange juice into a small bowl. Repeat with half of the remaining orange.
Squeeze the juice from the remaining orange half and from the lime into the small bowl. Whisk in oil in a thin steady stream until incorporated. Whisk in salt and pepper. Pour over salad and toss with 3 tablespoons of mint. Refrigerate for 20 minutes to allow flavors to blend.
Divide among salad plates and top with walnuts and remaining mint. Serve with toasted Panera Bread Three Seed bread.
Tip: For a nice peppery bite, serve the salad on a bed of baby arugula or watercress.