Preheat the oven to 400°F.

Line a large baking sheet with parchment paper. Set aside.

Slice the zucchini in half lengthwise. Use a spoon to scoop out the seeds, creating a 3/4-inch hollow. Arrange the zucchini cut side up on the prepared baking sheet.

Place an extra-large skillet over medium-high heat and add the olive oil. Once oil is hot, add the onion and ground beef. Cook, breaking up the meat with a spatula, until it is thoroughly browned and the onion is soft, 7-8 minutes. Add the garlic, Italian seasoning, salt, and black pepper and saute until fragrant, about 1 minute.

Remove the skillet from the heat. Add the petite diced tomatoes to the beef mixture and stir to combine.

Divide the beef mixture evenly among the zucchini halves, firmly packing it into the cavities.

Bake the zucchini boats on middle rack of oven for 15 minutes.

Open the oven and sprinkle each zucchini half with about a tablespoon of the shredded cheese. Continue baking until the cheese is melted and golden and the zucchini is fork-tender, 10-12 minutes.

Check to see that zucchini boats are done. Remove from oven or add time as needed.

Serve immediately.