Place squash, cut sides down, in baking pan; add 1/2 inch hot water. Bake, covered, at 400 degrees until squash is fork tender, 30 to 40 minutes. Remove squash from pan and turn cut sides up. Fluff strands of squash with tines of fork.
Saute green onions and garlic in margarine in small saucepan until tender, 3 to 4 minutes. Stir in broth and Italian seasoning; heat to boiling. Spoon half the mixture into each squash half and toss; sprinkle with Parmesan cheese and toss. Season to taste with salt and pepper.