Wash and prick the sweet potatoes all over with a fork. Rub with avocado oil, then wrap tightly in aluminum foil. Cook in your crockpot on low for 5-6 hours depending on the size of your potatoes. Mine were on the smaller side and took about 5 hours.
To make the pickled veggies, bring the water, vinegar, sugar and salt to a boil in a small sauce pan. This is a fume-y process, so open a couple windows. Stuff two pint jars to the brim with thinly sliced veggies. Add in fresh onion and smashed garlic cloves for more flavor. Pour the hot liquid over the vegetables until it reaches the top of each jar. Screw each lid on tightly and let cool at room temperature for one hour before transferring to the fridge. The pickles only get better with time and will be good in the fridge for about a month.
For the Greek yogurt cilantro sauce, blend together all the ingredients in your blender. This can also be made ahead and kept in a covered container in the fridge until the potatoes are ready.
Carefully remove the sweet potatoes from the crockpot and squeeze gently with a dish towel to determine softness. We want them fully cooked through. Unwrap the cooked sweet potatoes and slice into thick wedges. Heat a skillet over medium heat, then add in about a tablespoon of butter. Fry each side of the sweet potato discs until golden brown, salting each side after cooking. Add more butter as needed.
Next, heat the corn tortillas. I like mine with a little char, so I put them directly on the gas burner and use tongs to flip. You can heat them on a skillet as well with a little butter.
Build the tacos: sweet potato, tons of pickled veggies, a generous pour of yogurt cilantro sauce, topped with sliced green onion and a drizzle of lime juice. Serve with a side of spiced black beans. Enjoy!