Bring a pot of water to a boil and blanch the cabbage leaves for about 2 minutes until they are soft. Drain and set aside.
In a mixing bowl, combine mashed potatoes, capsicum, carrot, onion, green chili, coriander powder, salt, and coriander leaves. Mix well.
Take a cabbage leaf and place 2 tablespoons of filling at one end. Roll tightly, folding the sides in to secure the filling. Repeat for all leaves.
Heat oil in a pan and sauté the garlic until fragrant. Add tomato puree, black pepper, salt, and water, then simmer for 5 minutes.
Place the cabbage rolls in the pan, cover, and cook on low heat for 10 minutes, allowing the flavors to blend.
Remove from heat and serve warm, garnished with fresh coriander leaves.