Coat the bottom on a heavy pot with olive oil and place on medium heat.
Add the diced bell pepper and onion and cook for about 10 minutes until soft and translucent (but not brown).
Add the garlic and sauté for another minute.
Add the red pepper paste (or dried pepper) and the paprika and stir to coat everything.
Now add the tomatoes and cook for about one minute.
Add 1/2 cup dry white wine and cook for about one minute.
Add the potatoes, along with 2 cups of fish broth and 1 cup water.
Bring to a simmer and cook until the potatoes are tender (about 15 minutes).
Add a bit more broth or water if necessary.
Season with salt, pepper, and cayenne (optional).
Right before adding the tuna, use the back of a spoon to mash a few of the potatoes in the stew. This will release more starch and thicken the stew a bit more once the tuna is added
Add the cubes of tuna and let simmer for five minutes.
Remove from the heat and cover for 5-10 more minutes. Taste a piece of tuna to make sure it's fully cooked, and serve immediately.
Although it's not traditional, I sometimes serve this over basmati rice, which makes it last even longer!