Heat olive oil in a Dutch oven over medium-high; add onion, carrot, potatoes, garlic, salt, and pepper; cook, stirring often, until onions begin to soften, 5 to 7 minutes. Add stock, wine, and lemon juice; bring to a boil. Reduce heat to medium, and simmer 10 minutes; stir in tomatoes, and simmer until thickened, about 10 minutes. Gently stir in fish; cover, and simmer 5 minutes. Sprinkle with parsley; serve with grilled baguette slices.