Kosher salt and freshly ground black pepper, to taste
Fresh parsley, finely chopped, for serving (optional)
PREPARATION
Preheat oven to 400°F and grease a baking dish with nonstick spray.
Cut zucchini in half lengthwise, trim off stems, then use a spoon to scoop flesh from center of zucchinis. Chop up the flesh you scooped out and set aside.
Arrange zucchini halves in the prepared baking dish.
In a large pan over medium-high heat, heat the olive oil. Add onion and cook until starting to soften, 3-4 minutes. Add garlic and cook 30 seconds more. Add beef and cook until no longer pink, about 5 minutes.
Stir in marinara sauce, zucchini flesh, and season with salt and pepper. Let simmer 10 minutes.
Spoon mixture into zucchini halves and top with mozzarella cheese. Bake until cheese is bubbly and melted, about 20 minutes. Enjoy!