Combine the lentils and water in a small saucepan. Bring to a boil, then cover and simmer over low heat for about 20 minutes, or until tender. Drain, and set aside.
Preheat the oven to 375 degrees F (190 degrees C). Spray a pizza pan with non-stick cooking spray.
Heat oil in a skillet over medium heat. Stir in garlic and onions; cook until soft and slightly browned. Stir in eggplant and sweet potato. Pour in about 1/2 cup of liquid from canned tomatoes. Simmer until juices are absorbed.
Stir in tomatoes, ginger, curry powder, cumin, salt, and pepper; simmer until sweet potato begins to soften, about 15 to 20 minutes. (If juices cook off before potatoes are fully cooked, stir in a small amount of water, and cover.)
Place pizza crust on pizza pan. Spread the lentils evenly across the surface of the crust out to the edges. Spread sweet potato mixture evenly on top, and sprinkle with cheese.
Bake in a preheated oven until the edges are browned, about 10 to 13 minutes.