Heat grill to medium-high. Score the skin-side of the duck with a knife in a lattice pattern, being sure not to cut through to the flesh. Season each breast with salt and pepper on both sides.
Rub the skin side of each breast with a few tablespoons of the rub and place on the grill, rub side down, and grill until slightly charred and the skin begins to get crispy, about 4 to 5 minutes. Turn the breasts over, brush with some of the glaze and continue grill to medium-rare doneness, another 3 to 4 minutes. Remove the duck from the grill and brush with more of the glaze. Let rest for 5 minutes then slice 1/4-inch thick on the diagonal. Place the grilled green onions on a platter and top with the sliced duck breast. Serve with warm tortillas.
Asian Spice Rub:
2 tablespoons Spanish paprika
1 tablespoon dry mustard
2 teaspoons kosher salt
2 teaspoons ground black pepper
2 teaspoons ground star anise
2 teaspoons ground ginger
1 teaspoon ground allspice
1/4 teaspoon ground red pepper
Combine all ingredients in a small bowl.
2 tablespoons peanut oil
2-inch piece ginger, finely chopped
6 cloves garlic, finely chopped
2 tablespoons hot Asian chili paste, (recommended: Sambal Oelek)
1/2 cup honey
1/4 cup low-sodium soy sauce
Heat oil in a small saucepan over medium heat. Add ginger and garlic and cook until soft. Add the chili paste and cook for 1 minute. Whisk in the honey and soy and cook until just combined and the honey has melted. Let cool before using.