Preheat oven to 375 degrees.
Heat olive oil in a large skillet over medium-high heat. Add onions and saute until golden about 5 minutes, then add garlic and saute 30 seconds longer, transfer onion mixture to a plate. Brown meat (drain well) and season with salt and pepper.
Reduce heat to medium-low, add tomatoes, onion mixture, black beans, corn, chili powder, cumin, cilantro, lime juice and season with salt and pepper to taste. Cook just until heated through.
Add the mixture equally to each zucchini half (and slightly press as filling to fit). Cover baking dish with foil and bake about 15-20 minutes, until. Remove foil, sprinkle tops evenly with cheese then return to oven to bake until cheese has melted, about 3 minutes longer.
Enjoy!