Boil or microwave your potatoes until they are tender, about 20 - 25 mins depending on the size of your chunks of potato, then drain. Allow to steam dry for a minute or two, then place back in the pot/bowl they came out of, which should by now have steamed dry as well.
Mash potatoes using a potato masher, potato ricer or fork to your desired consistency. Add butter, sour cream, powdered garlic, and lemon zest then mix lightly to incorporate and melt butter.
Add milk 1 tbsp at a time until you reach your desired consistency, then fold through parsley, chives, shallots & baby spinach. If you boiled your potatoes on the stove in step 1, then transfer your potato mixture to a microwave safe bowl/dish.
Microwave potato mixture on high for 2-3 mins or until well heated, then fold through crumbled feta, add salt & pepper to taste and serve.