In a mixing bowl, combine grated lauki, besan, ginger, garlic, red chili powder, turmeric powder, chopped green chili, salt, and coriander leaves. Mix well into a thick batter.
Heat oil in a deep pan. Shape the mixture into small balls and deep fry on medium heat until golden brown. Remove and set aside.
To make the gravy, heat mustard oil in a pan, add onions, ginger, and garlic, and sauté until golden. Add tomatoes and cook until soft.
Add cashews, raisins (if using), and cook for 2–3 minutes. Let the mixture cool, then blend into a smooth paste.
In the same pan, heat 2 tablespoons oil, add the paste, red chili powder, turmeric, salt, and kasuri methi. Sauté until the oil separates.
Add reserved lauki water and adjust the consistency of the gravy. Bring it to a simmer.
Gently place the fried koftas into the gravy, stir lightly to coat, cover, and cook on low flame for 7–8 minutes so the flavors soak in.
Sprinkle garam masala and garnish with fresh coriander leaves before serving.