Add cider vinegar and sugar, and stir. Sprinkle mixture with the flour, and stir again for another 2 minutes so the flour cooks a little. Add the Swiss chard and stir until it is wilted down. Add chicken stock, bring up to a bubble, then simmer for a few minutes until the mixture is cooked and has thickened. Remove from the heat.
Boil sweet potatoes until tender, drain and reserve. Return the pot to the stove top over medium heat. Add butter and bananas to the pot.
Cook bananas in the butter for 5 minutes, then add the orange juice and zest to the pot. Allow the juice to cook out, 1 more minute. Add cooked, reserved potatoes back to the pot and add the heavy cream. Mash everything together. Season with the nutmeg, salt, and pepper to your taste. To the meat and veggie mixture, add the peas and the parsley, and stir to combine.
Pour into a baking dish, top with the mashed sweet potatoes and spread them out evenly. Transfer to the oven and bake until the top of the potatoes are lightly browned, about 15-20 minutes.