Heat half of the olive oil in a skillet or grill pan over medium-high heat. Slice acorn squash into thin moons, season with salt and pepper, and place in pan. Cook until tender (about 10 minutes per side). In a small bowl, whisk apple cider vinegar, remaining olive oil, and salt and set aside. In a large bowl, combine arugula, apples, pumpkin seeds, and squash. Toss with dressing, divide, and serve.