In a large bowl, add sliced radishes, olive oil, salt, pepper, garlic powder, and sliced onions. Toss radishes making sure all slices are coated.
In a saucepan, add butter, cream cheese, chicken broth, heavy cream, and shredded parmesan cheese over low-medium heat. Let the sauce simmer for 5 minutes.
Add ceinoated radishes to the 9"x13" dish. Pour cream sauce over radishes.
Top radishes with shredded Monterey Jack cheese.
Bake in the oven for 40-45 minutes. Cover the dish with foil if the cheese topping starts to brown too quickly