Chop the onion in semicircles. Cut the two peppers into strips. Slice the cloves of garlic. Place everything in a pan, sprinkle with olive oil and season with salt. Sauté all the ingredients until tender. Then add the potatoes, chopped in cubes, and water.When the potatoes are almost done, place the tuna espinheta in the pan and leave it to simmer. When done, sprinkle with chopped fresh coriander.