Slice the onions and fry in oil until soft. Peel the tomatoes in boiling water (or use tinned tomatoes). Slice and add to the onions.
Wash, trim and chop the spinach coarsely. Add to the stew and cook, covered, over a medium heat for 5 minutes, stirring to prevent sticking.
Thin the peanut butter with hot water to make a smooth paste. Add to the stew. Season with salt and pepper and cook for another 5 - 10 minutes, stirring and adding water if necessary to prevent sticking.