To get the closest taste to Cá Mòi Hộp without using the actual canned version itself, I would recommend sardines in olive oil or spring water. You'll need to add more tomato sauce/ketchup in its place and season accordingly. For the spring water version, drain the liquid out so its water doesn't dilute any flavor. If you cook with the olive oil one, pour the olive oil in to cook the onions instead of the oil suggested on the recipe list.