If using ground peanuts, grind them into a fine paste using a food processor. If using peanut butter, ensure it's natural and unsweetened.
In a large pot, heat the vegetable oil over medium heat.
Add the finely chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and ginger, and cook for another minute until fragrant.
Add the chopped tomatoes and green bell pepper to the pot.
Stir in the ground cumin and ground coriander.
Cook for about 5-7 minutes, until the tomatoes have softened and the mixture is well combined.
Add the ground peanuts or peanut butter to the pot.
Gradually pour in the water or chicken broth, stirring constantly to create a smooth sauce.
Bring the mixture to a gentle simmer.
Reduce the heat to low and let the sauce simmer for about 20-30 minutes, stirring occasionally. The sauce should thicken and the flavors should meld together.
Season with salt and black pepper to taste.
Transfer the groundnut sauce to a serving dish.
Garnish with fresh cilantro or parsley if desired.
Enjoy your meal!