Place the black-eyed peas and water in a large pot. Bring to a boil, then simmer for 45 to 60 minutes, until tender. Drain, reserving 1 cup of cooking liquid.
Season the beans lightly with salt and set aside.
Make the red red:
Heat the palm oil in a large skillet over medium heat. Cook the onion for 5 minutes, then add the garlic, ginger, and chili.
Stir in the tomatoes, tomato paste, paprika, cayenne, and salt. Simmer for 12 minutes until thickened.
Fold in the cooked beans and enough reserved cooking liquid to make a thick stew. Simmer for 10 minutes.
Fry the plantains:
Heat the neutral oil in a skillet. Fry the plantain slices in batches until golden on both sides, then drain briefly.
Serve the red red with fried plantains and sliced red onion.
Notes
Red palm oil gives the dish its signature color and flavor; use a mild palm oil if available.
For a faster version, use two drained cans of black-eyed peas.