Heat the oven to 400F.
Place the butternut squash, onion, 2 tablespoons olive oil, and ¼ teaspoon kosher salt on a rimmed baking sheet, tossing to combine.
Roast for 20 minutes, flip, and continue roasting until golden, about 10-15 minutes more.
Meanwhile, mix the pepitas, maple syrup, cinnamon, 1 teaspoon olive oil, and ¼ teaspoon salt in a small bowl. Add to a parchment or foil lined pie plate or small, heat proof baking dish.
Roast the pumpkin seeds for 10-15 minutes, stirring once, until lightly browned. Remove from the pan and allow to cool on a parchment lined plate (if you leave them in the pan they may stick and be difficult to remove once cool).
Make the dressing by whisking the lemon juice, salt, garlic, and olive oil in a small bowl until well combined.
Assemble the salad by placing the arugula in a large bowl. Add the roasted squash, onions, and apples. Pour over half the dressing and toss to combine. Add additional dressing to taste (store any leftover dressing in the fridge for another use.
Top with roasted pumpkin seeds, and serve.