Grate 1/4 tsp. zest from top of an orange. Slice 1/2-inch slice off top of oranges and carve out pulp; slice enough off bottom of oranges so they won't roll. Slice pulp of four oranges into half moons (1 1/2 cups); set aside. Juice rest of pulp (1/4 cup); set aside.
Cut a jack-o'-lantern face on each orange.
Whisk together reserved orange zest and juice with vinegar, maple syrup, mustard, lemon juice, ginger, pepper and salt. Whisk oil in until combined.
Toss greens and reserved orange pieces with 2 to 3 Tbsp. dressing. Stuff orange shells with salad; top with pumpkin seeds.