Preheat oven to 375°F (190°C).
Slice zucchini lengthwise and scoop out centers, leaving about a ¼-inch border.
Place zucchini cut-side up on a baking sheet, brush with olive oil, and season with salt and pepper.
Bake for 10–12 minutes, then remove and blot excess moisture.
Heat olive oil in a skillet over medium heat.
Add onion and cook until softened, then add garlic and cook briefly.
Add ground turkey and cook until browned, breaking it up as it cooks.
Stir in taco seasoning and broth or water; simmer 5–7 minutes until slightly thickened.
Stir in corn and black beans if using.
Spoon filling evenly into zucchini halves.
Sprinkle cheese over the top.
Bake uncovered for 18–22 minutes, until cheese is melted and bubbly.
Broil for 2–3 minutes if a more golden top is desired.
Rest 5 minutes before serving.