In a large, heavy skillet or stew pot, fry the onions in the butter until they are golden brown. With a slotted spoon, remove about 1/3 of the slices and set aside. Add to the pot the ginger, garlic and chili paste, and fry for 5 or 6 minutes, stirring constantly. Then add the lentils, green peas, carrots and green beans. Reduce heat to cook for 15 minutes, adding more butter, or a bit of oil , if necessary.
Add tomatoes, spices and mint, and stir for 5 minutes. Then pour in about a cu[p of hot water, cover and simmer unitl vegetables are about half cooked. Add rice, potatoes, salt, and another 4-5 cups of hot water (use lesser amount if you r vegetables have created quite a bit of liquid). Cover again, and cook for another 20-30 minutes until rice is done and water is absorbed .
To serve, garnish with the reserved onion slices, and pass around a bowl of yogurt as a sauce.