Prep the oven and pan. Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment or lightly grease a 9x13-inch baking dish.
Hollow the zucchini. Trim the ends and slice each zucchini in half lengthwise.
Use a spoon to scoop out the center seeds, leaving about 1/4 inch of flesh to form “boats.” Reserve about half of the scooped zucchini flesh, finely chop it, and set aside. Pat the boats dry with paper towels.
Season and par-bake the boats. Brush the zucchini halves with olive oil, then sprinkle with salt and pepper. Place cut side up and bake for 10–12 minutes until just tender but still holding shape.
This helps prevent soggy bowls.
Cook the beef. While the zucchini bakes, heat a large skillet over medium-high. Add a drizzle of olive oil and the ground beef. Cook, breaking it up, until browned and no longer pink, about 5–7 minutes.
Drain excess fat if needed.
Sauté aromatics and seasoning. Add the chopped onion to the skillet and cook 2–3 minutes until softened. Stir in the garlic and cook 30 seconds until fragrant. Sprinkle in the taco seasoning and stir to coat the beef.
Add mix-ins. Stir in the chopped reserved zucchini flesh, black beans, corn, and salsa.
Simmer 2–3 minutes to warm through and thicken slightly. Taste and adjust salt and pepper. The mixture should be juicy but not watery.
Fill the boats. Remove the zucchini from the oven.
Spoon the beef mixture evenly into each boat, pressing gently so it’s well-packed and mounded.
Add cheese and bake. Top each boat with shredded cheese. Return to the oven for 8–10 minutes, until the zucchini is tender and the cheese is melted and bubbly.
Finish and serve. Squeeze fresh lime over the hot zucchini boats. Add your favorite toppings—cilantro, avocado, sour cream, jalapeños, or extra salsa—and serve right away.