1. Place a large piece of foil directly over heat source on grill. Place a medium ovenproof pot on foil and heat until warm. Add oil, garlic, and scallion whites, and season with salt and pepper. Cook, stirring, until scallions begin to soften, about 2 minutes. Add tomatoes, black-eyed peas, and water. Season with salt and pepper. Cook, stirring occasionally, until tomatoes begin to break down, about 10 minutes. Add scallion greens and serve.