Grate the lemon zest and mix with flour.
In a sauté pan on medium low heat, add minced shallots and sauté for 2-3 minutes or until tender. Add 1 cup fava beans and sauté for 2 minutes. Add chicken stock. Bring to a boil and reduce heat and let simmer for 2-3 minutes. Add mixture to blender and cover. If the top of the blender fits air tight, leave it tilted to the side. (The hot liquid and steam will blow the lid off of the blender once turned on.) Blend the pea mixture on high heat until smooth and creamy. Season with salt and pepper to taste. Remove from blender and keep warm. If not used within 15 to 20 minutes, cool in ice bath and reheat when ready to serve.
Season with salt and white pepper on both sides. Preheat a large sauté pan on medium high heat. Add oil and place halibut in pan skin side up. Reduce heat to medium low. Sauté for 2-3 minutes or until halibut starts to turn golden brown. Flip fish and cook for 3-5 additional minutes. If you like your fish well done, lower the heat and cook longer or place into oven for a few minutes at 300 degrees. While the fish is cooking, preheat a large sauté pan on high heat. Add one ounce of olive oil. Once the oil starts to smoke, add mushrooms and reduce the heat to medium. Sauté for 2-3 minutes. Add shallots and sauté until lightly golden brown, about 2-3 additional minutes. Add peas and sauté for one minute and add chicken stock and let reduce until almost dry and the peas are tender. Add butter and parsley and season with salt and pepper to taste. Reserve for plating.
On a large plate, place a dollop of the fava bean purée in the center of the plate. Using the back of a spoon, press the spoon down and in a circular pattern, spread the purée out creating a small circle. Place the fish in the center of the purée and spoon the vegetables in two or three piles and some on top of the fish. Repeat for remaining plates.