In a medium-size saucepan, boil sweet potatoes until fork-tender, 10-15 minutes. Drain, cover, and chill until ready to use.
In a large mixing bowl, combine black beans, eggs, bread crumbs, corn, onions, cilantro, garlic, taco seasoning, and salt + pepper. Mash with a fork (if mixture is too dry, add some of the reserved bean liquid). Add corn and sweet potatoes and gently shape into patties and cover; chill at least 1 hour and up to 1 day.
Heat oil in a large pan over medium-high. Cook the patties for 5 minutes on each side. Transfer to platter.
Serve sliders with cilantro mayo on top of a bed of greens, or in a bun. Enjoy!
Cilantro Mayo:
Combine all ingredients and refrigerate until ready to use.
Notes
To bake burgers instead of pan-frying, place patties on a parchment paper-lined sheet pan and bake at 375°F. for 10 minutes on each side.