Place the peas, butter, water and salt in a saucepan and cover. Bring over medium heat and cook for 12-15 minutes, stirring occasionally, until peas are softened. Uncover the pan and remove from heat. Use a potato masher to mush the peas to your desired consistency (mostly mushy with a little bit of chunky for texture is my preference). You may want to add another 1-3 tablespoons of water at this point to reach the consistency you like (I added 2 tablespoons). Add the lemon zest and pepper to taste and stir in to combine.