Melt butter over medium heat in a large pot. Sauté the onion then the garlic for five minutes.
Add chopped broccoli to the pot and cook for five minutes. Then add the water, salt and pepper. Cover and let cook for five more minutes.
In a blender, add the avocado, lime, cilantro and mint. Then careful ladle in spoonfuls of the broccoli mixture. Blend until smooth, it should take a minute or two. Take time to scrap down the sides, give it a good stir and blend to make sure all is mixed.
Serve with chopped avocado and fresh mint or cilantro.