Heat oil in a pressure cooker and sauté onions until lightly golden.
Add mustard seeds, cumin seeds, kalonji, and dried red chilies; let them crackle.
Add potatoes and mix well.
Add tomatoes and stir.
Add all spices and chicken stock cube; cook 2 minutes.
Add ½ cup water, cover, and pressure cook 5 minutes on medium flame.
Release pressure and garnish with coriander, green chilies, kasuri methi, black pepper, and lemon juice.
Serve hot.