Preheat your oven to 375 degrees F.
Place the cubed potatoes in a large saucepan and fill with just enough water that it covers the potatoes. Add a 1/2 teaspoon of salt and heat over medium-high heat. Boil the potatoes for 20-25 minutes, or until they are tender. Strain through a colander and set aside.
While your potatoes are boiling, add the bacon to a non-stick saute pan over medium heat. Cook the bacon until crisp then transfer it to a paper-towel lined plate. Leaving the bacon grease in the pan and the stovetop set to medium heat, add the diced jalapeño and chipotle peppers. Cook for 2-3 minutes or until slightly tender. Remove from heat and set aside.
To a bowl, add the sweet potatoes, half and half and 4 tablespoons of butter. Using a hand mixer, blend the ingredients together until they are mashed and creamy. Season with salt and pepper and fold in the bacon and jalapeño/chipotle mixture. Once combined, pour the potatoes into an oven safe baking dish (9x13 inch casserole dish). Set aside.
In the bowl of your food processor, add the vanilla wafer cookies. Pulse 5-6 times and transfer to a large bowl. Add the panko and walnuts and stir to combine. Gently drizzle in the butter and fold again to combine. Spoon the crumble on top of the potatoes and place in the oven. Bake for 20-25 minutes or until the top is golden brown. If you find that the potatoes aren''t brown enough for your liking, place under the broiler set to low for 3-4 minutes until it reaches the level of brown you want.
Top with green onions and serve immediately. Enjoy!