Bring a large pot of cold water with salt to a boil over high heat. Add the spaghetti and cook, stirring occasionally until al dente, tender but not mushy, about 8 minutes. Drain and toss in 1 tablespoon of olive oil, set aside until sauce is ready. In a large saucepan heat oil over medium-high heat. Sauté onion and garlic until tender and translucent, about 3 minutes. Reduce heat, stir in pumpkin soup and simmer until soup is heated through, about 3 minutes. Season to taste with salt and pepper. Stir in parmesan, pasta; toss to coat. Serve warm garnished with pepitas.