Soak chana dal in water for 2 hours. Drain water and transfer it to a small or medium size pressure cooker. Add salt and 3/4 cup water and pressure-cook it for 2 whistles over medium flame. Based on the size of a pressure cooker, you may need to cook for longer or lesser time. Do not over cook the chana dal.
Open the lid of cooker and transfer cooked chana dal to a colander to remove excess water. Cooked chana dal should be whole and separated from each other. Let it cool for 10 minutes.
Prepare filling for tikkis by mixing cooked chana dal, dry mango powder, garam masala powder and red chilli powder in a bowl.
Take mashed potatoes in a large bowl. Add chopped green chilli, corn flour, lemon juice and salt and mix well.
Divide prepared mixture into 12 equal portions. Give each portion a round shape of ball and press a little to make 1/3 inch thick pattie. Put 1-2 teaspoons filling in the center of pattie.
Wrap filling from all sides and make round ball. Again press a little and flatten stuffed ball into pattie. Repeat the process
Heat a non-stick frying pan over medium flame. Drizzle 1-2 teaspoons oil over it. Put 5-6 tikkis over it and cook until bottom surface turns golden brown, approx. 2-3 minutes.
Turn it up side down, drizzle some oil around its circular edge and cook another side for 2-3 minutes until it turns golden brown.
another side for 2-3 minutes until it turns golden brown. Transfer it to a plate.. Stuffed aloo tikkis for chaats are ready.
Take 2-3 aloo tikkis in a serving plate.
Top each tikki with 1 teaspoon green chutney, 2 teaspoons date-tamarind chutney
Sprinkle onion and sev over it followed by 2 teaspoons beaten curd. Sprinkle red chilli powder and chaat masala powder over it.