In a bowl, combine all ingredients. Season with salt and pepper. Set aside.
Preheat one side of the grill, setting burner to high. Oil the grate.
In a bowl, combine all ingredients. With your hands, shape four patties.
Grill patties for about 4 minutes per side or until cooked through.
Toast buns. Spread the inside of buns with mustard. Drizzle herb sour cream generously on bottom buns. Top with patties. Garnish with melon slices and fennel. Drizzle with lime juice. Cover with top buns.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.