Heat the oil in a saucepan over medium flame. Add the onion and saute until translucent. Add the tomatoes and simmer about 5 minutes to cook them down.
Stir in the remaining ingredients and lightly mash the peas with the back of a spoon. Bring to a boil, then reduce heat to medium-low and simmer about 10 minutes, stirring occasionally. Add more water as needed to get a stew-like consistency.