1. First, heat a pan with olive oil on medium heat and add the onions and garlic. Cook until softened.
2. Then, add the bell peppers and cook for around 4-5 minutes or until softened.
3. Next, add the tomatoes and cook until they begin to soften. Now add the smoked paprika and potatoes.
4. Add the white wine and cook until the alcohol has evaporated.
5. Add 500ml of hot fish stock and 300ml of hot water so that it covers the potatoes. Add more water or stock if necessary.
6. Then, season with salt and pepper to taste and add fresh parsley, leaving some for the garnish.
7. Bring to a boil, then cover, lower the heat and let simmer for around 30 minutes, or until the vegetables are cooked to your liking. If you like a thicker stew, you can mash some of the potatoes now, to release starch into the stew.
8. Add the pieces of tuna, cover with the lid and put on low heat. The tuna should cook within a few minutes and turn from a red to light pink colour. Try a piece of tuna to check if it is cooked. Make sure not to overcook the tuna.
9. Finally, serve with fresh parsley and enjoy!