Slice the top and bottom off of the sweet potatoes, and slice potatoes in half crosswise. Rest each half on the broader end, then slice 3 times vertically and horizontally. Turn the potatoes on their side and make 4 or five more slices, to form cubes.
Transfer the sweet potatoes to a baking sheet, then add the oil, rosemary, salt, and pepper. Toss to coat evenly.
Bake for 35-40 minutes, until the sweet potatoes are tender and starting to brown around the edges.
Let cool for 5 minutes. Garnish with chopped parsley before serving.