When adding canned diced tomatoes to a recipe using Taco Seasoning Mix, bear in mind that diced tomatoes generally have around 1/4 cup of tomato juice packed with them. Adjust water amounts added to a recipe accordingly to not have the final result a little soupier than anticipated.
In fact, as a sidenote, if you have some tomato juice in the refridgerator - use that in the Taco Seasoning Mix versus water, as called for in the instructions, for a little more flavor.