Follow these steps to create your perfect Stuffed Zucchini Boats with Beef:

1. Preheat Oven and Prepare Baking Sheet: Preheat your oven to 400°F (200°C). Lightly grease a large baking sheet or a 9×13 inch baking dish. This will prevent the zucchini boats from sticking and make cleanup easier.
2. Prepare the Zucchini Boats:
   • Wash the zucchini thoroughly. Trim off the stem ends.
   • Slice each zucchini in half lengthwise.
   • Using a spoon or a melon baller, carefully scoop out the flesh from the center of each zucchini half, leaving about a ¼ to ½-inch thick shell. Be gentle to avoid piercing the skin. The scooped-out zucchini flesh is valuable! Don’t discard it. Chop it finely (about 1 to 1 ½ cups) and set it aside to be added to the beef filling later. This minimizes waste and adds extra vegetable goodness and moisture to the stuffing.
3. Pre-Bake Zucchini Shells (Optional but Recommended):
   • Arrange the hollowed-out zucchini shells, cut-side up, on the prepared baking sheet or dish.
   • Lightly brush the insides and cut edges of the zucchini shells with 1 tablespoon of olive oil. Season them lightly with a pinch of salt and pepper. This initial seasoning of the zucchini itself makes a big difference in the overall flavor.
   • Bake the empty shells for 10-15 minutes. This step helps to tenderize the zucchini slightly and removes some excess moisture, preventing the final dish from being too watery. They should be slightly softened but still hold their shape.
4. Prepare the Beef Filling:
   • While the zucchini shells are pre-baking (or if you skip that step, start here), heat the remaining 1 tablespoon of olive oil in a large skillet or Dutch oven over medium-high heat.
   • Add the finely chopped yellow onion and cook, stirring occasionally, until softened and translucent, about 4-5 minutes.
   • Add the minced garlic and cook for another minute until fragrant, being careful not to burn it. The aroma at this stage is already incredible!
   • Add the lean ground beef to the skillet. Break it apart with a spoon and cook, stirring frequently, until it’s browned and no longer pink, about 7-10 minutes.
   • If your beef has released a lot of fat, carefully drain off the excess. This keeps the filling rich in flavor but not greasy.
5. Add Flavor to the Filling:
   • Stir in the chopped zucchini flesh that you set aside earlier. Cook for about 3-5 minutes, allowing it to soften and integrate with the beef mixture.
   • Add the undrained diced tomatoes, tomato paste, Italian seasoning, salt, black pepper, and optional red pepper flakes to the skillet. Stir everything together thoroughly to combine.
   • Bring the mixture to a gentle simmer. Reduce the heat to medium-low, cover the skillet, and let it simmer for 10-15 minutes. This allows the flavors to meld together beautifully and the sauce to thicken slightly. Taste and adjust seasonings if necessary. You want a rich, savory filling.
6. Stuff the Zucchini Boats:
   • Once the filling has simmered and the zucchini shells have been pre-baked (if you chose that step), remove the shells from the oven. If any water has accumulated in the shells during pre-baking, carefully pour it out.
   • Generously spoon the beef mixture evenly into each zucchini boat. Don’t be afraid to mound it up slightly, as it will settle a bit during baking. Ensure each boat is well-filled for a hearty serving.
7. Top with Cheese and Bake:
   • Sprinkle the shredded mozzarella cheese evenly over the top of the beef filling in each zucchini boat.
   • Follow with a sprinkle of grated Parmesan cheese over the mozzarella. The Parmesan adds a nice salty crust.
   • Return the stuffed zucchini boats to the preheated oven (still at 400°F / 200°C).
   • Bake for 20-25 minutes, or until the zucchini is tender (easily pierced with a fork), the filling is heated through, and the cheese is melted, bubbly, and lightly golden brown. If the cheese starts to brown too quickly, you can loosely tent the dish with aluminum foil for the last 5-10 minutes of baking.
8. Rest and Garnish:
   • Once baked to perfection, carefully remove the Stuffed Zucchini Boats with Beef from the oven.
   • Let them rest for 5-10 minutes before serving. This allows the filling to set slightly and the boats to cool down just enough to be handled and enjoyed without burning your mouth.
   • Garnish with freshly chopped parsley or basil just before serving for a pop of color and fresh flavor.