Brown ground beef over medium heat in a large skillet, breaking up the meat into small crumbles as it cooks.
Once meat is cooked through and nicely browned, spoon off and discard any excess fat.
Add taco seasoning mix, tomato sauce and water to the skillet. Increase heat slightly and bring mixture to a simmer.
Simmer, stirring occasionally, until all the excess liquid has cooked off and you have a thick meat mixture, similar to the consistency of a thick chili.
Place flour tortillas on a smooth work surface.
Add a layer of grated cheese to each tortilla.
Add a generous heaping of the taco seasoned beef to each tortilla.
Spoon on taco sauce.
Top with more shredded cheese.
Roll up each tortilla to enclose the filling. Be sure to fold in the ends so the filling doesn't leak out.
Wrap each Meximelt in a damp paper towel.
Microwave 2 Meximelts at a time on high for 1 minute or until cheese has completely melted.
Serve with a side of sour cream if desired.