Heat 1 teaspoon of vegetable oil in a flat pan over medium-low heat.
Add gram flour to the pan and fry until it turns slightly brown and fragrant, stirring very frequently.
Remove the roasted flour to a medium mixing bowl and let it cool down for 5 minutes.
Add coriander powder, turmeric powder, chili powder, fennel powder, mango powder, and salt to the roasted gram flour and mix well.
Rinse the chilies with water and wipe them dry using a kitchen towel. Make slits in the green chilies with ends intact and remove their seeds. Stuff the green chilies with the gram flour mixture.
Heat 2 tablespoons of oil in a pan over medium heat.
Arrange the chilies in the pan in a single layer. If all the chilies are not fitting, then cook them in batches.
Cover the pan with a lid and cook for 4-5 minutes until the chilies are charred from the bottom.
Flip the chilies using a pair of tongs. Cover and cook for another 4-5 minutes.
Remove on a serving plate and serve hot.