Preheat oven to 400°F (200°C).
Slice zucchini lengthwise and scoop out the centers slightly to create boats.
Brush zucchini with olive oil and season with salt and pepper. Place on a baking sheet.
Heat a skillet over medium heat and cook ground beef or turkey with diced onion until browned. Drain excess grease if needed.
Add garlic and cook for 1 minute.
Stir in taco seasoning and tomato sauce or salsa. Simmer for 2–3 minutes.
Spoon taco filling evenly into zucchini boats.
Top with shredded cheese.
Bake for 18–22 minutes until zucchini is tender and cheese is melted and bubbly.
Remove from oven and add desired toppings before serving.