ROAST the sweet potato: Cut into cubes and toss with olive oil. Spread out on a baking sheet and roast at 425°F for 25-30 minutes until tender.
PREP the pickled onions: Add thinly sliced red onions to a bowl and toss with lime juice and salt. Let marinate for at least 10 minutes. Leftovers can be stored covered in the fridge for about 3 days.
MAKE the Cilantro Lime Sauce: Add all ingredients to a blender and blend until combined. Adjust taste with more salt, pepper, or lime juice as desired. Store leftover sauce in the fridge for up to five days.
ASSEMBLE salad by adding lettuce, sweet potatoes, and black beans to a mixing bowl. Add as many pickled onions as you like and drizzle some cilantro lime sauce on top. Toss until well combined.