Preheat oven to 350*. In large saucepan, cook squash and onions in small amount of water for 5-10 min until softened-careful, you do not want mush! Save some cooking for in the oven! Drain and set aside. In a med. sauce pan, melt margarine over med heat. Stir in flour. You may play with this a bit if too thick add marg., if too thin add flour. When well blended and thickening, add in milk, slowly, stirring continually. Cook and stir until bubbly and smooth thickness. Remove from heat. Stir in the cheese until well blended. Place squash/onions in prepared baking dish, pour cheese mixture over and gently mix. Sprinkle with parmesan cheese and bake for about 20 min. (sorry, I lost the back page of my recipe with the nutrient breakdown, but I know this fits as a low – cal/South Beach option).