Optional: Soak potatoes in water to cover for up to 1 hour. Drain and pat dry.
Preheat the oven to 400F. Toss the potatoes with spices and olive oil. Place them on a nonstick baking sheet in a single layer.
Roast the potatoes, lentils, and tomatoes for about 30 minutes, or until golden brown. Toss them after 15 minutes. Remove the potatoes once they are fork tender, the lentils once crispy, and the tomatoes once they have burst.