1. To make the relish, warm the olive oil in a medium saucepan over a medium heat and add the onions, garlic, ginger, and red chilli. Cook for 5 minutes until translucent. Add the sugar, turmeric, coriander, and lime juice. Cook for 20 minutes over a low heat, until thickened and reduced. Allow to cool completely. Add the lime zest and season with salt.
2. Next prepare the crispy shallots. Toast the fennel seeds, coriander seeds, and chilli in a pan over a medium heat for 1-2 minutes or until fragrant. Using a pestle and mortar, grind the toasted seeds and chilli to a fine powder. Add to a bowl with the ginger and sea salt.
3. Preheat a deep fat fryer or large saucepan no more than half filled with the grapeseed oil until 160°C, or until a cube of bread browns in 60 seconds. Using a mandolin, thinly slice whole rings of shallot (or use a very sharp knife). Pat dry on kitchen paper, then deep fry in batches if necessary, for 2-3 minutes until golden brown and crispy. Remove with a slotted spoon and drain on kitchen paper. While hot, season with the spiced salt mix.
4. Preheat the barbecue. Cook the sausages according to pack instructions. Slice the buns in half, being careful not to slice through completely. Toast lightly for 1 minute, on the barbecue. Spoon half of the relish into the buns. Place the sausage on top, then add the remaining relish. Sprinkle with crispy shallots and freshly chopped coriander on top.