Crush sage leaves, garlic, and pepper in a mortar and pestle to make a paste. Mix with lemon juice and olive oil in a bowl. Marinate duck breast for at least 2 hours.

Grill the duck breast over medium-high heat, turning once, until it reaches an internal temperature of 130 degrees. Cover with aluminum foil for 5 minutes.

Preheat the grill to 400 degrees.

Place the pizza crust on a pizza pan and top with mozzarella cheese and chopped sage.

Thinly slice the duck breast and add it to the pizza.

Grill the pizza until the cheese melts and the crust is cooked, about 10 minutes.

Slice and serve the pizza.