Preheat oven to 350 degrees.Make the herb butter by combining butter, parsley, chives, lemon zest, sea salt and black pepper. Mix well.Slice baguette into about 1" slices and place on a baking sheet. Bake for about 5-8 minutes to lighly toast.Cut the radishes into thin slices while the bread is baking.Remove bread from oven and allow to cool for a few minutes. Top with herb butter, arugula and sliced radishes. Optional: Add a pinch of salt, chives and parsley for garnish.