Melt the butter in a large stock pot over medium heat. Add the onion, and cook until the onion has softened and turned translucent, about 5 minutes. Add the potatoes and garlic, and continue cooking until the potatoes have softened slightly, about 10 minutes
Pour in the chicken stock, tomatoes, and carrots. Bring to a boil, then reduce heat to medium-low, cover, and simmer for 10 minutes. Add the evaporated milk, season to taste with salt and pepper, then stir in the halibut and the bacon. Continue simmering uncovered until the halibut is flaky and no longer translucent in the center, about 10 minutes. If you use cheese then this would be the point to stir in the Cheddar cheese until the cheese has melted. Serve immediately