If you have a gas hob, turn on a large hob and set it to medium. Place the pepper directly on the flame and cook it for 10 mins, turning every so often with tongs till blackened all over. Alternatively, heat your grill to high. Halve the pepper and grill it, cut-side down, for 10-15 mins till blackened and charred.
When the pepper is charred all over, pop it in a bowl and cover the top with cling film. Set aside for 15 mins to cool.
Slice the thick cores out of the kale leaves. Roughly chop the leaves and put in a large heatproof bowl. Add the sun dried tomatoes. Peel and roughly chop the garlic and add that too. Pour in enough boiling water to cover everything. Set aside for 10 mins to soak.
While the kale soaks, tip the walnuts into a dry frying pan. Set over a medium heat and toast for 2-3 mins, shaking the pan now and then, till they’re browned and smell nutty. Tip into a food processor.
Add the breadcrumbs to the warm pan and stir for 1 min till golden. Tip them into the processor as well. Drain the kale, tomatoes and garlic (keep the water), and add them to the processor. Put a large pan of salted water onto boil.
Peel the charred skin off the pepper (it’s fine if a few black bits cling on). Scrape out the seeds. Roughly chop the pepper and add to the processor with 1 tbsp oil and 2 tbsp of the reserved kale soaking water. Season with plenty of salt and pepper. Blitz to make a chunky pesto.
Add the spaghetti to the boiling water. Simmer for 8-10 mins till the spaghetti is cooked but not too soft – it should still have a little chew. Drain, then tip back into the pan and add the pesto. Toss together and warm for 2-3 mins, then serve in warm bowls.