Preheat oven to 350°F. Grease a 9x13 casserole dish and set aside.
Heat a large skillet over medium-high heat and add frozen zucchini spirals.
Cover and let cook, 6 minutes.
Remove the lid and flip. Season with salt and pepper and cook an additional 3 minutes.
Drain the zucchini in a mesh sieve.
Meanwhile, heat a medium saucepan over medium-high heat.
Add the onion and ground beef. Season with salt and pepper.
Cook until browned, about 6 minutes.
Mix in the minced garlic and cook until fragrant, 30 seconds.
Drain the fat from the ground beef and mix in the marinara sauce.
Bring to a boil and then reduce heat to a simmer. Simmer for 10 minutes.
Once the meat sauce is cooked, start building your baked ziti dish.
Start with half of the cooked zucchini spirals in an even layer in the prepared casserole dish.
Spread half of the sauce over the zucchini and sprinkle with 1/2 cup mozzarella and 1/2 cup cheddar cheese.
Repeat with remaining zucchini, sauce, and cheese.
Sprinkle parmesan cheese over the top.
Place casserole in oven and bake, uncovered for 30 minutes, until cheese is melted and sauce is bubbling around the edges.