Crack eggs in a bowl and whisk it well. Keep aside.
Heat oil and butter in a heavy bottom pan or a non-stick skillet over medium flame. When it is hot, add cumin seeds and let them crackle.
Add chopped onions and saute well till it turns translucent.
Add ginger-garlic paste and green chilies. Saute until the raw aroma goes away.
Add in chopped tomatoes and cook until they turn soft.
Turn the flame to low and add salt, turmeric powder, red chili powder, garam masala or pav bhaji masala. Mix well and cook for a minute.
Add the whisked eggs and gently mix. Let it sit without stirring for 30 seconds.
Turn the flame to medium and scramble the eggs by moving the whisked eggs across the pan and over onto themselves well to mix along with onion-tomato masala. Scrape the sides of the pan into the center and mix it well.
Lastly, add coriander leaves and give a mix.
Cut open the pav. Heat a sliver of butter in the pan.
Place the pav and vigorously rub the pav around the pan so that any eggy flavors left behind are absorbed by the pav.