Once the meatballs are browned, warm the marinara sauce in a large, wide saute pan over medium-low heat. Add the meatballs and simmer while you prepare the polenta and the greens.
Make the polenta
Whisk the polenta, water, and salt in a medium saucepan and simmer over medium heat for 10 minutes. Reduce to low and whisk in the milk, stirring occasionally until very creamy and loose. The polenta will continue to thicken as it sits. Stir in the butter and taste for seasoning, adding more salt as desired. If desired, add in the parmesan cheese.
While the polenta is cooking, make the greens. Remove the stems from the Swiss chard and slice very thinly, then roll the leaves and slice into very thin ribbons.
Heat the olive oil in a large skillet over medium heat. Add the stems and cook until just tender, about 5 minutes. Add the garlic and salt and cook another 30 seconds, then add in the leaves and cook another 2-3 minutes, until just wilted and tender. Season, adding more salt/pepper as desired.
Serve! Divide the polenta among 4 bowls, then top with the meatballs and garlicky chard. Spoon on more marinara sauce, as desired.