Place a heavy medium or large tawa on the stove top. First heat it on a medium flame. When the tawa gets hot, reduce the flame to a low.
Add 2 tablespoons butter. You can also use oil instead of butter.
Add ¼ teaspoon ajwain (carom seeds) and ¼ teaspoon cumin seeds. Saute for a few seconds. Ajwain gives a good aroma in the dish. If you do not have carom seeds, then just skip it.
Next add ⅓ cup heaped finely chopped onions.
Stir and begin saute on a low to medium flame, till the onions turn translucent.
Then add ginger-garlic paste. Saute till the raw aroma of ginger-garlic goes away.
Now add 1 cup finely chopped tomatoes and 1 to 2 green chillies, chopped. Mix well and then lower the flame.
Cover the onion-tomato mixture with a lid and cook on a low flame for 4 to 5 minutes. Do check once or twice when the tomatoes are cooking, just to make sure that the masala mixture is not sticking on the tawa.
After 4 to 5 minutes, the tomatoes would have softened.
Using a veggie or potato masher, mash the tomatoes once they have softened.
You don't need to make a smooth mush of the tomatoes. Just roughly mash the tomatoes.
Next add ½ cup finely chopped capsicum. Mix very well.
Saute the capsicum for 2 to 3 minutes on a low flame.
Then add ¼ teaspoon turmeric powder, ½ teaspoon coriander powder, ½ to 1 teaspoon kashmiri red chilli powder and 1 teaspoon pav bhaji masala. If you do not have pav bhaji masala, then add ½ teaspoon garam masala and ¼ teaspoon dry mango powder.
Mix the spice powders very well.
Now add 2 cups of sliced or chopped white button mushrooms. You can also use cremini or portobello mushrooms. Stir and mix the mushrooms with the masala and saute for 2 to 3 minutes.
Then season with salt as per taste. Mix again very well.
Add ½ cup water and mix again.
Cover the mushroom mixture with a lid. On a low flame simmer till the mushrooms are tender and cooked well.
It will take about 10 to 12 minutes for the mushrooms to cook. Do check a couple of times and if the water looks dried up, you can add some more water. If there is too much of gravy or water in the dish, then cook till all of the water evaporates. This tawa mushroom masala is dry to semi-dry dish with no gravy.
Next step is to add ¼ cup coriander leaves and ¼ teaspoon kasuri methi (dry fenugreek leaves). Skip kasuri methi, if you do not have it.
Mix very well and saute for a minute. Switch off the flame.
Serve with rotis or bread or as a side dish with dal-rice.