This is a Kenyan dish to be served over rice. The relatively authentic version depicted here has an interesting flavour, but is a bit bland. Consider departing from slavish authenticity and jazzing it up with some dried red pepper flakes, Tabasco sauce, and / or fresh cilantro leaves.
Instead of fresh tomatoes, you can use 2 cups (16 oz / 450g) of tinned diced tomatoes. Don't drain.Instead of peanut butter, you can use the same quantity of ground or finely chopped peanuts, or try some peanut butter powder,