Preheat the oven to 200°C/400°F/gas mark 6 and line a baking tray with baking paper. Pulse the cauliflower in a food processor until it resembles rice, then spread over the baking tray and place in the oven for 8-10 minutes until it turns brown at the edges, stirring every few minutes. Keep warm.
Make the katsu sauce next. Heat 1 tbsp of the oil in a wok or shallow pan to medium heat and gently saute the onions for around 8-10 minutes or until golden and softened.
Add the ginger and garlic and cook for another 4-5 minutes. Add the curry powder and garam masala and stir through until fragrant.
Add the carrot, potato, soy sauce and agave. Add just enough stock to come up halfway to the mix. You may not need to use all the stock. Bring to the boil, then lower the heat to simmer gently for around 20-25 minutes. Stir occasionally until the sauce is thickened and the potatoes are soft. Transfer to a blender or use a stick blender to blitz to a smooth puree. Return to the pan to keep warm and loosen with a little stock depending on how thick you prefer the sauce to be.
Meanwhile, prepare the chicken breast. Season the flour with black pepper and use it to dust the chicken, ensuring even coverage. Heat the remaining oil in a an ovenproof frying pan, then brown the chicken on both sides until a deep golden colour. Place in the oven for a final 7-8 minutes until cooked though.
When ready to serve, thickly slice the chicken and serve with the curry sauce and cauliflower rice.