In a large, deep skillet over medium-high heat, brown the mushrooms in the butter for 5 minutes. Sprinkle with the flour and cook for 1 more minute while stirring. Add the broth, milk and mushroom soup. Bring to a boil, whisking constantly, until the sauce thickens. Simmer for 2 minutes. Remove from the heat. Add the tuna, peas and lemon zest. Season with salt and pepper. Mix well.
