Meanwhile, melt the butter in a skillet over medium heat. Stir in the green onions, red bell pepper, garlic, and red pepper flakes until the vegetables have softened, about 5 minutes. Pour in the white wine, and season with dill and tarragon. Simmer for 2 minutes, then add the chicken broth, half-and-half, Parmesan cheese, and remaining 1 tablespoon of lemon juice; season with salt and pepper to taste. Bring to a boil over medium-high heat, then dissolve the flour into the water, and stir into the boiling sauce. Return to a boil, then reduce the heat to medium-low, and simmer until the sauce has thickened, about 10 minutes. Spoon the sauce over the halibut to serve.