Cut the eel into about 3-cm (approximately 1 1/4-inch) pieces. Season with salt and pepper. Rinse the sage leaves and pat dry.
Preheat the broiler. Thread pieces of eel and sage leaves, alternating them, on small wooden skewers. Mix mustard, lemon juice, and oil and coat the skewers. Broil on oiled rack (with drip catcher underneath), turning, for about 8–10 minutes.
Serve with toasted garlic bread.