In a large, deep sauté pan over medium heat, combine potatoes, cauliflower, peas, tomatoes, and ¼ cup water. Season with salt, cover, and cook for about 15 minutes, until vegetables are softened. Smash the cooked vegetables into a pulp using a potato masher, then transfer to a large bowl.
In the same pan, sauté chorizo over low heat for 2-3 minutes. Deglaze the pan with a little water and cook until the water has evaporated. Remove half the chorizo oil and set aside for the chorizo butter.
Add butter and cumin seeds to the pan, followed by red onions. Sauté for 1-2 minutes, then add cilantro, capsicum, garlic paste, kasuri methi, turmeric, Kashmiri chili powder, and pav bhaji masala. Sauté for another 1-2 minutes.
Stir in lime juice and the smashed vegetables. Cover and cook for 4-5 minutes. Uncover and smash the bhaji until combined. Season with salt and remove from heat.
Mix together 50g butter, reserved chorizo oil, and 1 tsp pav bhaji masala in a bowl.
Butter the bread buns (Pav) on both sides with the chorizo butter then toast on a pan on both sides until toasted.
Serve the Bhaji with the bread buns toasted in chorizo butter, diced raw onions mixed with cilantro, and a wedge of lime.