1. Soak chana dal in warm water for 20 mins.
2. Mean while finely chop banana stem and squeeze out any excess water.
3. Coarsely grind soaked chana dal with garlic, red chilli and fennel seeds.
4. In a large bowl combine ground chana dal, chopped banana stem, minced onion, curry leaves, hing, cooking soda, rice flour and required salt. Mix well.
5. Heat oil in a kadai to deep fry, shape prepared batter into medium sized vadas. Drop 3 to 5 vadas in hot oil, reduce heat and cook on medium heat until vadas turn golden and crispy and bubbling stops.
6. Drain banana stem vadas on paper towel.
7. Serve hot banana stem vadas with coconut chutney.