Preheat the oven to 400°F (200°C), slice the zucchini lengthwise, and scoop out enough center flesh to create sturdy boat-shaped shells.
Arrange the shells in a baking dish, brush lightly with olive oil, and bake for 8–10 minutes while preparing the filling.
Heat a skillet over medium heat and cook the ground turkey or beef until browned, breaking it into small pieces as it cooks.
Stir in the taco seasoning, black beans, corn, and diced tomatoes, then simmer for several minutes until the mixture is hot and slightly thickened.
Remove the zucchini shells from the oven and spoon the taco filling generously into each hollowed center.
Sprinkle shredded cheese over the top and bake for another 12–15 minutes until the zucchini is tender and the cheese is melted.
Finish with chopped cilantro and serve with salsa, avocado, Greek yogurt, or fresh lime wedges.