In a large stock pot or Dutch oven
, heat oil to shimmering. Add the onion and cook for about 7 minutes, stirring occassionally on medium-low or until softened. Add the garlic and cook for one minute, until fragrant. Stir in harissa and tomato paste, stirring to coat the onions for one minute. Add the ,dried (and soaked) black-eyed peas, and water. Bring to a boil, then turn down to low to simmer. Place a lid on the pot and cook for 40 minutes.
If using canned or already cooked black eyed peas (about 2 C / 260g), drain peas, reduce water to about 1 cup, skip cooking for 40 minutes and continue on with the recipe.