Preheat the oven to 350°F (175°C).
In a skillet over medium heat, add the diced onion and minced garlic. Sauté until the onion becomes translucent.
Add the ground beef to the skillet, breaking it apart with a spoon. Cook until browned and fully cooked, about 7-10 minutes.
Drain any excess fat, then stir in the diced tomatoes, chili powder, cumin, salt, and black pepper. Cook for another 2-3 minutes to combine flavors.
Remove from heat and mix in half of the shredded cheese and cilantro.
If using zucchini, slice them lengthwise and remove some of the inner flesh to create a 'boat.' If using low-carb tortillas, set them aside for filling.
Spoon an equal amount of the beef mixture into each zucchini boat or tortilla, then roll or fold them tightly.
Place the filled zucchini boats or tortillas in a baking dish. Pour the enchilada sauce evenly over the top and then sprinkle with the remaining cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for about 15 minutes. Then, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let cool slightly. Garnish with extra cilantro before serving.