Prep the oven and pan: Preheat your oven to 400°F (200°C). Line a large baking sheet or 9x13-inch baking dish with parchment for easy cleanup.
Prep the zucchini: Trim the ends and slice each zucchini lengthwise. Use a spoon to scoop out the seeds and some flesh to form “boats,” leaving about 1/4 inch around the edges.
Reserve about 1/2 cup of the scooped flesh, finely chopped.
Season the boats: Place zucchini cut side up on the pan. Brush with olive oil and season with a pinch of salt and pepper.
Par-roast the zucchini: Roast for 10–12 minutes until slightly tender but not fully cooked. This helps them hold their shape once filled.
Cook the filling: While the zucchini roasts, heat a large skillet over medium-high.
Add the ground meat and cook, breaking it up, until mostly browned. Drain excess fat if needed.
Add aromatics: Stir in the diced onion, reserved chopped zucchini flesh, and garlic. Cook 3–4 minutes until softened and fragrant.
Season and simmer: Sprinkle in taco seasoning, then add salsa, black beans, and corn.
Stir and simmer 2–3 minutes until thick and cohesive. Taste and adjust salt and pepper.
Fill the boats: Spoon the taco mixture into each zucchini, packing it to the top. Don’t be shy—overfill a little for a hearty bite.
Add cheese: Sprinkle shredded cheese evenly over the tops.
Bake to finish: Return the pan to the oven and bake 8–10 minutes, until the cheese is melted and bubbly and zucchini are fork-tender.
Top and serve: Let cool 2–3 minutes.
Add your favorite toppings like diced tomatoes, cilantro, jalapeños, and a dollop of sour cream or Greek yogurt. Squeeze lime over the top for brightness.