Fill a large, shallow pan 1/4 full with water and a bit of salt; bring to a boil. Cut each zucchini in half lengthwise and place face down in the water. Cover and cook 4 to 5 minutes only- until crisp-tender. Remove from pan and let cool.
Meanwhile, cook sausage in a skillet until browned. Add onion, cook until opaque and then add cream cheese and corn, stirring until cheese is melted.
Remove pan from heat and gently stir in tomato and 1/2 cup of the Parmesan cheese.
Scoop out the center of each zucchini half and fill with the sausage mixture. Place the filled zucchini in an oiled baking pan.
Sprinkle the remaining grated Parmesan over the filled zucchini. Bake in a 350 degree oven for 20 to 25 minutes.