Combine 1 cup of the orange juice and 1/4 cup of the vinegar in a large zip close plastic bag; add the duck. Squeeze out the air and seal the bag; turn to coat the duck. Refrigerate, turning the bag occasionally, at least 2 hours or overnight. Drain and discard the marinade.

Spray the grill rack with nonstick spray; prepare the grill.

Meanwhile, to prepare the glaze, combine the shallots, wine or broth, the remaining 1/4 cup each orange juice and vinegar, the orange zest, salt, and pepper in a medium saucepan; bring to a boil. Reduce the heat and simmer, watching carefully and stirring occasionally, until the mixture is reduced by half, about 15 minutes. Remove from the heat.

Grill the duck, turning once and basting with the glaze, until the juices run clear when pierced with a fork, about 8 minutes per side.

Transfer the duck to a carving board; let cool slightly. Thinly slice lengthwise. Arrange the slices on serving plates and drizzle with any leftover glaze. Serve each portion with 1/3 cup of the arugula, if using.

Makes 8 Servings