Prep zucchini by cutting off stem end and lightly trimming off blossom end. Cut each zucchini in half.
Fill a large, shallow pan 1/4 full with water and a bit of salt and bring to a boil over high heat. Cut each zucchini in half lengthwise and place face down in the water (as much as possible). Reduce heat to medium; cover and cook 1 to 3 minutes only, just until crisp-tender. Remove from pan to a cutting board and let cool.
Preheat oven to 350 degrees.
Meanwhile, cook sausage over medium heat in a large skillet until browned. Add onion and garlic, cooking until onion is opaque, Mix in cream cheese and corn, stirring until cheese is melted.
Remove pan from heat and gently stir in the diced 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 a greased baking pan.**
Sprinkle the remaining grated cheese over the filled zucchini. Bake in a 350 degree oven for 20 minutes, until cheese is melted and filling is warmed through. Serve immediately.
*If not using a paste tomato, remove seeds from tomato and squeeze some juice out before dicing.**If you have any filling remaining that won't fit in the zucchini, just place it around the pan to serve as extra with the zucchini.To Freeze for Later Meals:
Complete the recipe through to the stuffing, place on a baking sheet, but instead of baking, place it in the freezer to freeze until firm, 2-3 hours.
Remove the zucchini boats and place in a gallon freezer bag (about 4 fit in each), remove air, label, and freeze for 3-4 months.
To use, thaw overnight in the fridge and bake as directed.