Preheat oven to degrees 375 degrees F.

Pierce holes in potatoes using a fork. Roast sweet potatoes and purple potatoes on a baking sheet in the oven until tender, about 30 minutes.

Meanwhile, steam corn in a steamer basket until tender, about 5 minutes.

Remove from oven; set aside to cool for at least 10 minutes then cut potatoes into 1/2 inch cubes.

In a large bowl, combine cooked potatoes, corn, spinach and walnuts.

In a small bowl, whisk lemon juice, zest, olive oil, vinegar, maple syrup or honey, sea salt and pepper; drizzle over potato mixture and serve warm or at room temperature.