To cut parsnips: Trim tops and bottoms; peel (optional), and slice in half crosswise to separate thick and narrow parts. Halve or quarter thick parts lengthwise, until all parsnip pieces are roughly the same size (this ensures even cooking).
To cut sweet potatoes: Slice into ¼-inch long slices, then into ¼-inch long strips with a knife or crinkle-cut knife.
In a large bowl, add parsnips and sweet potatoes. Toss with olive oil, paprika, salt, and pepper
On a large rimmed baking sheets, spread parsnips and sweet potatoes in a single layer.
Roast until tender and golden brown, 25 to 30 minutes, rotating baking sheets and tossing halfway through baking time.