Blend the tomatoes, peppers, and onion into a smooth purée.
Heat the oil in a pot and add the purée. Cook for about 10 minutes, stirring occasionally.
Stir in seasoning cubes, salt, and any protein being used.
Stir in the water and bring to a boil.
Gently stir in the cubed yam. Cover and simmer, stirring occasionally, until the yam becomes soft and some of it has broken down to thicken the dish.
Add leafy vegetables if desired and cook for an additional 3–5 minutes.
Adjust seasoning and remove from heat.