Butter 2 mini muffin tins, or use 1 tin and bake in 2 batches. In a small saucepan, melt the butter over low heat. Meanwhile, in a large bowl, combine the oats, coconut, walnuts, and flour and mix. Stir the honey into the melted butter and bring to a boil, stirring often. Pour the butter mixture over the dry ingredients and mix well. Press 1 heaping tablespoon of the mixture into each mini muffin cup. Bake until just beginning to brown, 15 to 20 minutes. Remove from the oven and immediately press a walnut half on top of each honey bunch. Let cool 10 minutes in the pan, then transfer to a wire rack and cool completely. Store in an airtight container.