Place the onions, gram flour, lemon juice, cumin, coriander seeds, green chilli, chopped coriander and baking powder in a mixing bowl.
Season with salt and add a few tablespoons of water to form a thick batter that coats the onion.
Leave to rest for 15 minutes and then, using your fingers, mix again to combine thoroughly.
Preheat the oven to 220°C/200°C Fan/Gas 7.
Line a baking sheet with baking parchment and, using your fingers or a dessert spoon, drop small mounds of the mixture onto the prepared baking sheet to give you 12 bhajis.
Spray with low calorie cooking spray and bake for 15-20 minutes until golden.
Remove from the oven and serve immediately.