Preheat oven to 400 degrees F. Toss the cauliflower florets with 2 tablespoons oil, salt and pepper. Arrange them in a single layer on a large baking sheet. Roast the cauliflower in the oven until lightly golden brown, about 25-30 minutes. Set aside.
Heat 2 tablespoons oil in a large saucepan over medium heat. Add the onion and saute until tender, about 6-7 minutes. Add the garlic and dried oregano leaves and saute until fragrant, about 1 minute. Add the chicken broth, cauliflower and 1 1/2 cups water.
Cover the saucepan and bring to a boil. Reduce the heat to medium-low and simmer for 20 minutes. Then puree in a food processor or with a stick blender until smooth. Return to the saucepan, add milk and cook over medium heat for 5 minutes. Add the cheese, stir well and let it melt. Season with salt and pepper. Garnish with black pepper and serve with French bread.
Note: If soup is too thick, add more milk.