Preheat the oven to 450 F. While waiting for the oven to heat, heat 2 cups of water to boiling while you slice the red onion into thin slices. Place the onion in a colander in the sink and slowly pour the boiling water over the onion slices to soften and slightly cook them. Add the vinegar, sea salt, and sugar to a small bowl or glass container and stir to dissolve the salt and sugar. Then add the onion slices to the vinegar and stir to submerge them. Set aside.
Remove the chicken from the marinade and put into a baking dish or on a baking pan lined with parchment paper. Put into the oven and set the timer for 15 minutes.
Peel and shred the sweet potato using a box grater or food processor with the grating blade. Place the shredded sweet potato on a baking sheet lined with parchment paper, drizzle the oil and sea salt on top and then using your hands or a spoon, mix. Spread the sweet potato evenly on the sheet and put into the oven with the chicken for 10 minutes.
While the sweet potato and chicken are cooking, toast the coconut chips by placing them in a dry pan over medium heat. Start stirring them occasionally after about 3 minutes and continue to cook until they are lightly toasted and the ends have turned brown.
While everything is cooking, put all of the ingredients for the Mango Dressing into a food processor or blender and blend until smooth and creamy. You may want to add up to an additional 1/4 cup of oil to make it runnier, totally up to your preference on this. Without the extra 1/4 cup of oil it's a thick sauce.
Slice the cucumber and chop the cilantro and set aside.
Check the chicken after 15 minutes - the temperature should be 165 F in the thickest part if taken with an instant-read thermometer. If it isn't, continue to cook until it is. Once it's done, remove it from the oven and cover with aluminum foil or a kitchen towel for 5 minutes to rest.
Start to assemble the salads - divide the spring mix evenly between the plates. Add toasted coconut chips, shredded sweet potatoes, cucumbers, and cilantro to each plate. Using a fork, remove the pickled onions from the vinegar and place on each plate. Then once the chicken is done resting, slice and divide between the plates. Either dollop some of the sauce on each plate or serve on the side. Enjoy!