Put the parsnips and rutabaga in a 4-quart pot and submerge them in water by 2 inches. Cover the pot and bring the water to a boil over high heat. Uncover and boil the parsnips and rutabaga for 10 minutes, then add the sweet potatoes. Continue to boil until everything is fork-tender, about 10 minutes more.
Drain the veggies and transfer them to a medium mixing bowl.
Heat a small pan over low heat and add the coconut oil. When it is melted, sauté the ginger and garlic just until golden, about a minute. Add the ginger and garlic to the bowl of boiled root veg, along with the salt.
Mash everything very well, then taste and adjust for salt.