Heat the oil in a medium sized pot or a large pan and add the onion and peppers. Cook 5-6 minutes to soften.
Add the ginger-garlic paste and cook for 30 seconds, stirring.
Add the tomatoes and stir. Cook for 6-7 minutes, or until softened.
Add the ground Kashmiri red chilies (or other red chili powder), garam masala, turmeric, coriander, cumin, salt, chickpeas, potatoes, cauliflower, carrots, and peas. Stir.
Pour in 2 cup water, or enough to just cover the mixture. Bring to a boil, then reduce heat, cover, and simmer for 30 minutes, or until the mixture if very soft.
Use a large fork or potato masher to mash the pan mixture to your preference. You can also use a food processor or stick blender. Garnish with dollops of butter, chopped cilantro and onion with lemon wedges on the side.
For the Buns: Split the buns in half then generously butter both sides. Heat a skillet to medium-high heat and toast the buns, butter side down, 1-2 minutes, or until toasted. Serve.