Preheat oven to 450 degrees. On a rimmed baking sheet, toss together sweet potato, red onion, and olive oil. Roast until sweet potato is tender and browned in spots, about 20 minutes. Transfer to a large bowl and let cool completely.
Add tomato, avocado, cilantro, and lime juice. Season with salt and toss to combine.
Quick ways to enjoy this salsa: Serve with crackers or a toasted baguette for a snack. Scatter over chopped lettuce for a simple salad. Stir into couscous to create an easy side dish. Use as a topping for chicken tacos or nachos. Fold into scrambled eggs at breakfast.