Cook bacon in a medium skillet over moderately high heat until the fat is rendered, 3 to 5 min. Transfer bacon to paper towels, keeping the drippings in the skillet. Add the butter along with the garlic and 1/2 of the shallots to skillet. Cook over moderate heat until softened, about 2 min. Add cream cheese, Havarti, and whisk in whipping cream. Simmer until reduced by half, about 8 min. Season with salt and pepper.
Heat a large skillet over moderate heat. Add olive oil and sauté Swiss chard leaves with the remaining shallots until softened, about 3 min. Season with salt and pepper. Transfer chard leaves to a shallow baking dish and cover with the cream cheese mixture. Top with panko and crumbled bacon. Bake until crumbs are toasted and the casserole is bubbling, about 30 min.