Beet Greens with Potatoes and Nigella Seeds

Name: Beet Greens with Potatoes and Nigella Seeds
Ingredients: 2 tablespoons mustard oil (can be substituted with regular olive oil); 1 teaspoon nigella seeds; 1 small to medium red onion, very finely chopped; 1 teaspoon grated ginger; 2 fingerling potatoes, peeled and diced; ½ teaspoon turmeric; 1 teaspoon salt or to taste; ½ teaspoon sugar; 2 to 3 green chilies, slit; 2 cups finely chopped beet leaves