Preheat and prep the pan. Heat the oven to 400°F (200°C). Line a large baking sheet or 9x13-inch dish with parchment or lightly oil it.
Hollow the zucchini. Slice each zucchini lengthwise.
Use a spoon to scoop out the center to make “boats,” leaving about 1/4 inch of flesh around the sides. Chop about half of the scooped flesh to add to the filling; discard the rest or save for another recipe.
Season the boats. Brush the zucchini boats with olive oil and sprinkle lightly with salt and pepper. Arrange them cut side up on the prepared pan.
Sauté the aromatics. Warm a large skillet over medium heat.
Add a light drizzle of oil if needed, then sauté the onion for 3–4 minutes until softened. Stir in garlic for 30 seconds, just until fragrant.
Brown the protein. Add ground turkey to the skillet. Cook, breaking it up, for 5–7 minutes until no longer pink.
Drain excess fat if necessary.
Add spices and zucchini. Stir in chili powder, cumin, smoked paprika, oregano, salt, pepper, cayenne (if using), and the chopped zucchini flesh. Cook 2 minutes to bloom the spices.
Stir in sauce, beans, and corn. Pour in the tomato sauce, then add black beans and corn. Simmer for 2–3 minutes until slightly thickened.
Taste and adjust salt or heat.
Fill the boats. Spoon the taco mixture into each zucchini boat, packing it in. Use all the filling for generous portions.
Bake. Cover loosely with foil and bake for 15 minutes. Remove foil, sprinkle with cheese, and bake another 8–10 minutes until the zucchini is tender and the cheese is melted and bubbly.
Finish and serve. Let cool for 5 minutes.
Squeeze fresh lime over the top and add your favorite toppings. Serve warm.