Heat olive oil in a large pot over high heat on the grates of the grill. Stir in shallots and garlic and cook until tender. Stir in fennel and tomato, and continue cooking about 5 minutes. Add white wine and ouzo and reduce by half. Add the heavy cream and bring to a simmer. Stir in mussels, 1/2 the basil and season with salt and pepper. Cover the pan and cook until the mussels are open, discarding any that do not. Stir in the remaining basil and serve in large bowls with grilled bread.