Place a large nonstick skillet over medium-high heat. Add the onion and ground turkey into the skillet. Season with salt and pepper. Cook for 8 to 10 minutes, breaking apart with a wooden spoon or spatula while it cooks.
Add the marinara sauce to the turkey mixture. Stir to fully coat the turkey mixture with the sauce and cook for an additional 2-3 minutes.
Meanwhile, as the turkey cooks cut the zucchini in half, lengthwise. Use a spoon to scoop the seeds and center out of each zucchini half, leaving about ¼ inch thick zucchini boat.
Place the zucchini (cut-side up) in a 9x13 baking dish. Spoon the turkey mixture into the four zucchini boats. Sprinkle each boat with a little parmesan cheese, if desired.
Cover the baking dish with foil. Bake for 20-30 minutes or until boats are heated throughout and cheese has melted. Serve immediately while warm.
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Notes
Ground turkey: Swap with ground chicken for a similar lean protein option. Ground beef or mild or hot Italian sausage are also great alternatives if you want something with red meat. For a vegetarian or vegan alternative, try using crumbled tempeh.
Marinara sauce: Use your favorite pasta sauce flavor variation or swap it with pesto for pesto zucchini boats.
Parmesan cheese: You can swap this with mozzarella cheese for a creamy melt, cheddar for a sharper taste or feta for a tangy twist. For a dairy-free option, use nutritional yeast or a vegan cheese alternative to keep it plant-based.
Add veggies: Like I said feel free to add additional veggies to the turkey mixture. If you do this, make sure to add them with the onion so they can soften slightly.