Set the Instant Pot to the sauté setting.
Add 2 tbsp butter and 2 tbsp oil and 1 ½ tsp cumin seeds. As the oil heats, the cumin seeds will begin to sputter. Add green chilies and onions and allow the onions to soften for 2-3 minutes. Add ginger-garlic paste and stir to combine.
Note: To make the ginger-garlic paste, grate or grind 2 cloves garlic and ½ inch nub ginger.
Add 1 tsp fennel seeds, ½ tsp turmeric, 2 tsp cumin powder, 2 tsp coriander powder, 2 tsp red chili powder (to taste), 1 tsp amchur powder and stir to form a paste. Add 2 tsp Kashmiri red chili powder or paprika, optionally, for the red color.
Add tomatoes and allow them to cook down for 3-4 minutes. Add 1 tsp garam masala powder and the remaining vegetables. Add 1 cup water and 2 tsp salt (to taste).
Close the lid securely and set the Instant Pot to manual for 8 minutes. Make sure the vent is in the center sealing position. Quick release the pressure until the stopper goes down and it is safe to open.
Once the pav bhaji cools a little, mash it or pulse 2-3 times with an immersion blender.
Note: you do not need to puree, so just pulsing a few times will ensure you get the correct, chunky consistency.
Adjust seasoning to taste, adding more salt, red chili or garam masala as desired.
Set the Instant Pot to the sauté setting and allow the Pav Bhaji to cook for an additional 3-5 minutes with the lid slightly covering it.
Note: Be very careful, and keep it partially covered, as it will splatter.
Turn off and mix in 1 dollop of butter and a few squirts of lime or lemon juice.