Peel the onions and finely slice them. Halve the pepper and scoop out the seeds and membrane. Slice the pepper into strips. Peel the garlic cloves and finely chop them. Pick the rosemary leaves and finely chop them. Scrub the sweet potatoes and chop them into small chunks.
Pour 2 tbsp olive oil into a pan and warm to a medium heat. Slide in the chopped onions and pepper. Sprinkle in a pinch of salt and pepper and fry for 10-15 mins, stirring occasionally, till softened and golden.
Sprinkle in 1 tbsp Cajun seasoning, the chopped garlic and rosemary. Fry for a further 2 mins.
Pour in the chopped tomatoes. Drain the chickpeas and toss them into the pan. Slide in the sweet potatoes. Pour in 1 ltr boiling water and crumble in the stock cube. Stir well to combine. Bring the stew back to the boil, then reduce to a simmer and cook for 30 mins.
Stir the spinach into the stew. Grate in the lemon zest and squeeze in the juice from 1 half. Try the stew and add a little extra salt and pepper or lemon if needed. Leave the stew chunky, or to give the it a thicker texture, pulse a few times with a stick blender. Ladle the stew into bowls and serve with wedges of the remaining lemon half.