Drain the black-eyed peas and rinse them well. Transfer to a medium saucepan and add enough water to cover by 2 inches.
Bring to a boil over medium heat. Decrease the heat to medium-low, skim off any foam, and partially cover.
Simmer just until tender, 40 to 50 minutes. Stir in 1 tsp. of the salt and simmer for 5 minutes. Drain well.
Meanwhile, warm the oil in a medium saucepan over medium heat. Add the onion and sauté until soft, 5 to 7 minutes. Add the garlic, creole seasoning, and the remaining ½ tsp. salt and sauté until the garlic is fragrant, about 3 minutes.
Add the diced tomatoes, vegetable stock, and the black-eyed peas to the saucepan, stir, and bring to a simmer. Decrease the heat to medium-low, cover, and simmer, stirring occasionally, about 45 minutes. Taste and season with more salt if desired.