Preheat oven to 375 degrees. Wrap your 4-5 whole garlic cloves in foil. Roast for about 25 minutes until tender. Remove roasted garlic from skin and smash.
In a medium bowl, combine 2 cups heavy cream, 1/2 cup Parmesan cheese and 1/2 cup shredded Monterrey jack cheese, roasted garlic, and a 1/2 teaspoon of oregano, salt and pepper.
Thinly slice 4-5 small potatoes. You’ll want the potatoes to be about 4 times thinner than the zucchini, or about 1/16 of an inch. Slice 2 medium zucchinis, about 1/4 of an inch. Quarter 2 small onions and slice thinly.
Layer the zucchini, potatoes, and onions in a casserole dish or 4 individual casserole dishes. You’ll have more potatoes than the others, so I layer like this: 2 potatoes overlapping, zucchini, onion, and repeat.
Pour the cream mixture over the veggies, about 1/2 cup per individual dish or evenly over a larger baking dish. Top with remaining cheeses.
Bake at 400 degrees for about 30 (individual) to 45 minutes. Place small casserole dishes on a lined sheet pan for any possible overflow. Garnish with chopped parsley and enjoy!