1. In a large skillet, heat 1-2 tablespoons olive oil, then add the shallots and garlic. Sauté over medium heat for 3-4 minutes, until lightly browned. Stir in chard and cook until just wilted. Add salt and pepper to taste. Remove from heat and set aside.
2. Combine the coconut milk and tahini in a small pot over high heat. Whisk together, stirring constantly, until the mixture is at a rolling boil. Reduce heat and whisk in nutritional yeast and lemon juice. Season with salt to taste.
3. Layer the bottom of a 13×9 casserole dish with half the shingled sweet potatoes. Spread the swiss chard mixture evenly on top of the potatoes. Layer on the remaining sweet potatoes and top with the coconut/tahini mixture. Cover with aluminum foil and bake for 45 minutes. Remove and sprinkle with cheese, then bake for another 45 minutes, uncovered, until bubbling and most of the liquid has evaporated. Serve warm.