Preheat the oven to 200 degrees. Spread the diced pieces of the half sweet potato over a baking sheet. Roast the potato until tender and soft in about twenty minutes in the oven. Remove the baking sheet and let the pieces cool completely to room temperature.
Take a large plate and spread the fifty grams of arugula in an even layer across it. Arrange the cooled sweet potato pieces on the greens. Crumble the fifty grams of sheep's or goat's cheese by hand over the potato and arugula.
Scatter the tablespoon of roasted pine nuts over the dish. Drizzle the whole thing as a final step with the prepared dressing of lemon juice and olive oil. Serve the salad immediately after adding the dressing.