Preheat the oven to 375F and grease a 9x13-inch baking dish.
Wash the zucchini with warm soapy water. Trim the ends and slice each zucchini in half lengthwise. Use a spoon or a melon baller to scoop out the flesh, leaving the shell about ¼-inch thick. Put the zucchini meat inside a mesh strainer or between a few paper towels to absorb the moisture. Place the zucchini boats, cut side up, inside the baking sheet.
Make the filling:
Heat a large skillet over medium-high heat. Add the oil, and once hot, add the zucchini meat, black beans, corn, taco seasoning, and 1 ½ cups of salsa to the pan. Mix to combine and cook for about 5 minutes, until the mixture is heated through, turn off the heat.
Add half of the cheese to the meatless mixture and toss to combine.
Divide the cheesy meatless mixture among all the zucchini boats, making sure to fill them generously. Sprinkle the tops of the zucchini boats with the remaining cheese.
Bake:
Bake in the preheated oven for 30 minutes until the cheesy tops are melted and the sides of the zucchini feel soft when poked with a fork. Remove from the oven and serve.