Heat olive oil in a non-stick skillet. Cook and stir onion until fragrant, about 2 minutes. Add sweet potato and garlic; continue to cook and stir for 1 minute. Stir collard greens, ginger, and salt into onion mixture until vegetables begin to soften, about 3 minutes more.
Pour water into vegetables and cover skillet. Simmer until greens are tender, about 5 minutes.