Preheat oven to 425 degrees.
To prepare squash, use a sharp knife to cut acorn squash in half lengthwise.
Remove seeds with a spoon.
Slice squash into even pieces, and cut off skin.
Line a baking sheet with parchment paper.
Coat squash with olive oil, and sprinkle with salt and pepper.
Bake squash for 18-20 minutes. Allow to cool while arranging the salad.
Add arugula to a large bowl, and top with roasted squash, red onions, cranberries, and pumpkin seeds.
Toss with salad dressing of your choice, or with olive oil and lemon juice.