Bring a large saucepan full of water to a boil and add sweet potatoes. Cook until fork-tender, approximately 10-15 minutes. Drain and rinse under cold water to cool. Drain well. (You can also steam them instead of boiling).
Toast sunflower seeds in dry skillet over medium-high heat until golden and fragrant.
Combine apple, onion, cilantro, and lime juice in a large bowl. Stir in sweet potatoes and oil; add salt and pepper to taste. Stir in avocado and toasted sunflower seeds just before serving.
This salad tastes best the sooner you enjoy it; I recommend serving immediately or preparing it the night before to take as a lunch. If preparing in advance, store in the refrigerator in an air-tight container. The longer the ingredients sit in the dressing, the less pronounced the flavors and textures become.
If you don't like raw red onions, try substituting shallots. They're milder, with a bit less bite.