Prep the oven and pan. Preheat your oven to 400°F (200°C). Lightly oil a large baking dish or sheet pan to prevent sticking.

Hollow out the zucchinis. Trim the ends and slice each zucchini lengthwise. Use a spoon to scoop out the center seeds and flesh, leaving about 1/4 inch of zucchini shell. Chop about 1/2 cup of the scooped zucchini to add to the filling; discard the rest or save for another dish.

Season the boats. Place the zucchini halves cut-side up in the baking dish. Drizzle with a little olive oil and sprinkle with salt and pepper. Set aside.

Brown the beef. Heat olive oil in a large skillet over medium-high heat. Add the ground beef and cook, breaking it up with a spatula, until browned and no longer pink, about 5–7 minutes. Drain excess fat if needed.

Sauté aromatics. Add the chopped onion and the reserved chopped zucchini to the skillet. Cook until softened, 3–4 minutes. Stir in the garlic and cook for 30 seconds, until fragrant.

Build the sauce. Add diced tomatoes and tomato sauce. Season with oregano, basil, smoked paprika, red pepper flakes, salt, and pepper. Simmer 3–5 minutes to thicken slightly. Taste and adjust seasoning. If using rice, quinoa, corn, or beans, stir them in now.

Cheese it up. Stir in half of the Parmesan to enrich the filling. Remove from heat.

Fill the boats. Spoon the beef mixture evenly into each zucchini half, mounding it slightly. Top with shredded mozzarella and the remaining Parmesan.

Bake. Cover the dish loosely with foil and bake for 15 minutes. Remove the foil and bake another 8–12 minutes, until the zucchini is tender and the cheese is bubbly and lightly golden.

Finish and serve. Let the boats rest for 5 minutes. Garnish with fresh parsley or basil. Serve warm.