Pour a small drizzle of olive oil into a large saucepan over medium heat. When the oil is hot, tip in the bacon. Fry for 4 to 5 minutes, stirring occasionally, until all the fat has rendered and the bacon is crispy and golden brown.
Add the onion, season with salt and pepper (bearing in mind that the bacon is quite salty), and cook for another 5 minutes. Then add the potatoes with the stock, milk, and cayenne.
Bring to a boil, decrease the heat, and simmer for 3 minutes, or until the cubes of potato are half cooked. Add the fish and gently simmer for another 3 to 4 minutes, until the fish is opaque and the potatoes are tender. Season with salt and pepper to taste, stir in the chopped herbs, and serve.
You want to use about 8 oz of fish total use a balance/combination you like.