Wash, peel and cube the potatoes placing them in a large saucepan of cold water. Add enough water to cover them and bring to a boil, simmer until fork tender about 20 minutes.
Meanwhile heat the oil over medium-low heat in a medium frying pan. Add the garlic and a pinch or two of salt and pepper. Cook until fragrant 2 - 3 minutes.
Add the spinach, toss and turn off the heat. Add a couple more pinches of salt and pepper.
Once the potatoes are tender drain and add back to the pan, off the heat.
Add the butter and ½ cup milk, smash with a potato masher, adding more milk to get the consistency you like.
Stir in the spinach, feta, dill and zest. Season well with salt and pepper.