Preheat oven to 200°C. Peel the mangoes. Cut off slices from either side of the seed. Chop half of them into small cubes and roughly chop the rest. Put the roughly chopped mango into a mixer jar. Add half the chenna and grind till smooth. Transfer into a bowl. Put the remaining chenna in the mixer jar, add half the yogurt and grind till smooth. Transfer into the same bowl.
Grind the remaining yogurt with 4 tbsps sugar till smooth and add to the bowl. Mix everything well. Take oats in a bowl, add butter, 1 tbsp sugar and mix with hand. Add honey and mix again. Put this mixture into a spring form tin and press lightly and evenly. Bake in the preheated oven for 12-15 minutes. Add lemon rind to the mango-chenna mixture and mix well. Add mango cubes and mix. Heat mango juice in a small non stick pan, add some of it to the gelatine and stir till well blended.
Add the remaining juice and mix well. Cool and add to the mango-chenna mixture and mix well. Take the spring form tin out of the oven and let it cool down to room temperature. Pour the mango-chenna mixture into the spring form tin over the oats base and keep it in the refrigerator until completely set. Demould, cut into wedges and serve.