1. Preheat oven to 425ºF. Grease a 2 1/2 quart baking dish with cooking spray.
2. In a large microwave safe bowl, add the green beans and 1 inch of water. Cover and cook for 3 minutes. Drain. Set aside.
3. In a large skillet over medium-high heat, add 3 teaspoons of olive oil and the butter. Once butter is melted add onions and Mediterranean Seasoning. Cook until the onions are lightly brown, about 3 minutes.
4. Stir in the mushrooms, thyme, salt and pepper. Cook, stirring occasionally until the mushrooms have released their juices and the liquid has evaporated, 3 to 4 minutes. Pour in the sherry and cook until the liquid has evaporated, about 1 minute.
5. Sprinkle flour over the mushroom mixture and cook until flour is toasted, about 3 minutes. Whisk in broth and milk. Simmer stirring often until the sauce is thickened, about 4 minutes. Remove from the heat. Stir in the cheese and the green beans, stirring to combine. Transfer to the prepared dish.
6. In a small bowl stir together the panko, Shallots and paprika and the remaining ½ teaspoon olive oil. Sprinkle over the casserole. Bake for 20 minutes, or until the casserole is bubbling and golden brown.