Wash, scrub and dry sweet potatoes. Trim ends and cut potatoes into 1/4-inch rounds. Sprinkle with a pinch of salt, black pepper, chili powder and cumin.
Heat a large sauté pan over low-medium heat and add olive oil. Add sweet potato rounds and cook about 5 minutes on each side or until the rounds are tender and start to brown. Set aside.
Add avocado flesh to a bowl and squeeze with lime juice. Sprinkle with a pinch of salt and mash with a fork until smooth. Stir in yogurt. Set aside.
Place the rounds on a serving platter or plate. Top each one with a dollop of avocado cream, a sprinkling of cilantro and green onion. Add a few chopped nuts if using and enjoy.