Preheat the oven to 180°C (356°F).
Wash the zucchini and slice it thinly.
Finely chop the onion and mince the garlic.
In a large bowl, combine the zucchini, onion, garlic, cheddar cheese, eggs, milk, breadcrumbs, salt, and pepper.
Transfer the mixture into a greased oven-safe dish.
Evenly sprinkle cheddar cheese and breadcrumbs on top.
Bake in the oven at 180°C (356°F) for 25-30 minutes until done.