Heat oven to 450°F.
Place potatoes in a pot, cover with water, bring to a boil and cook to tender. Mash with milk, salt, pepper and cheese.
While water for the potatoes comes to a boil, heat a cast-iron skillet over medium-high heat. In a bowl, coat the chorizo, onion and olives with a liberal drizzle of EVOO. Add everything to the hot pan then transfer to the oven and roast 15 minutes, stirring once midway, until sausages are crisp and onion slices are tender.
Meanwhile, add 2 tablespoons EVOO to a skillet over medium to medium-high heat and add chopped garlic. Stir 2 minutes then wilt in chard. Season with salt, pepper, paprika, and nutmeg. Add stock to greens and braise 10 minutes.