Heat the oil in a large skillet over medium-high heat. Add the prawns and sauté until just cooked through, about 1 to 2 minutes per side. Transfer the prawns to a plate. Add the onion, bell pepper and garlic to the skillet and cook until softened, about 3 to 4 minutes. Mix in the tomatoes, corn, chipotle pepper and stock and simmer until the tomatoes start to break down and become saucy, about 5 minutes. Return the prawns to the skillet and heat through a minute or so. Toss in the oregano or cilantro, season with salt, and serve.