First we'll prepare thecha. Heat oil in a small pan, add cumin seeds. When they start to crackle add green chilli and fry them for 2 minutes with continuous stirring. Take out the green chilli in a mixture jar and add garlic cloves, fry them for 2 minutes with continuous stirring. Take out the garlic as well in jar. Add roasted peanuts and Salt and grind for just 5 seconds. It shouldn't become smooth paste.
Now we'll prepare vada. Heat oil in a pan and add mustard seeds, when they start to crackle, add chopped onion and fry till it become golden brown. Then add turmeric powder, Red chilli, mashed boiled potatoes, green chilli and salt. Mix them well and cook them for 2-3 minutes.
Now take gram flour, add water and Salt in it and form a paste. Paste should neither be much thick nor much thin. Now make small size balls of potato mixture. Heat oil in a pan, dip potato mixture balls in gram flour paste and then put them in oil to fry. Fry them till they become light brown in colour.
Finally take pav, cut them from the middle horizontally. Apply layer of thecha and put vada in heat. Serve hot maharashtrian famous vada pav with spicy thecha.
