Preheat oven to 400 degrees.
Slice the zucchini into half moons and add butter to a skillet to melt.
Once melted cook garlic and onion until translucent.
Add zucchini and cook until tender, about 5 minutes.
In a small bowl stir together the seasonings, eggs and Half and Half. Set aside.
Sprinkle half of the cheddar and half of the parmesan over the zucchini and onions.
Pour the egg and cream mixture over the zucchini.
Sprinkle the remaining cheese over the top.
Bake for about 15 minutes or until center is set.
Sprinkle freshly chopped parsley before serving if desired.