Step 1Heat the oven to 400 degrees. In a large skillet over medium-high heat, melt 2 tablespoons butter. Coarsely chop the kale and add it to the skillet. Cook, stirring constantly, until it softens and reduces, about 2 to 3 minutes. Season generously with one-half teaspoon salt, reduce the heat to low and cook, covered, another 2 to 3 minutes until it is quite tender. Reserve.
Step 2Place the cranberries in a small bowl, add the orange liqueur and set aside to soften, at least 10 minutes. Melt the remaining one-half cup butter in a small skillet with the orange zest. Set aside.
Step 3Rinse the game hens and pat them dry. Season each generously inside and out with one-fourth teaspoon salt and a grind of pepper. Brush them lightly with some of the orange butter.
Step 4In a large bowl, combine the kale, the cranberries with their liqueur, the remaining orange butter, the walnuts and a generous grinding of pepper and stir to combine. Stuff the cavities of the game hens with the kale mixture.
Step 5Tie the birds' leg ends together with kitchen twine to hold the shape and keep the stuffing from spilling out. Arrange the birds on a rack in a roasting pan and cook until a thermometer inserted in the deepest part of the thigh reaches 150 degrees, 30 to 35 minutes, for medium-well; or 160 degrees, 40 to 45 minutes, for well-done. Remove from the oven and let rest 5 minutes before serving.