Heat the olive oil in a heavy-bottomed pan or a Dutch oven over medium-high heat. Add in the potato slices. Cook the potatoes until they start to soften, this will take anywhere from 5-10 minutes depending on the size of the potatoes. Add the fennel and sauté until softened, about 3 minutes. Add in more oil if needed and add the garlic, sautéing for about a minute. Add a pinch of salt and grind of pepper. Add the wine and let it almost completely evaporate from the pan, about 4-5 minutes. Add a generous 2 (plus) cups of water to the pan and bring it to a boil. Reduce the heat and simmer the stew until the potatoes are soft. Add in the fish chunks and cover the pot. Reduce the heat to low and let the fish simmer slowly until cooked through, about 5-7 minutes depending on thickness. Season the stew with salt and pepper. Stir in the dill and finish with a squeeze of lemon juice.