1red bell pepperribs and seeds removed, finely diced
1poblano pepperribs and seeds removed, finely diced
1jalapeno or fresno chile pepperribs and seeds removed, minced
2large garlic clovesminced
1/2teaspoonred chile flakes
1large russet potatoabout 1 pound, peeled and cut into 1-inch cubes
3cupsfish stock or water
2tablespoonsfinely chopped parsley
Heat 1 tablespoon of the oil in a large heavy bottomed saucepan or Dutch oven. Season the tuna with salt and sear it in batches over high heat until browned on at least two sides, about 2 minutes total. Remove to a plate.
Add the remaining oil and the onion, peppers, garlic, chile flakes, and 1 teaspoon salt. Saute over medium heat until the vegetables are very soft but not browning, about 10 minutes. Stir in the tomatoes and potatoes. Cover with the stock or water and bring to a boil. Turn the heat down to medium-low and simmer until the potatoes are tender and the broth has thickened, about 15 to 20 minutes. Taste for seasoning and add more salt as necessary.
Stir in half the parsley and the tuna. remove from the heat and let stand 3 minutes, until the tuna is heated through and just barely cooked.
Serve the stew in bowls and garnish with the remaining parsley.