Heat a skillet over medium and cook the ground beef, breaking it into small pieces, until browned and no longer pink, about 7 minutes. Drain off excess fat.
Return the skillet to the stove, stir in the taco seasoning and water, and let the mixture simmer briefly—about 1–2 minutes—so the seasoning dissolves and coats the meat.
Transfer the seasoned beef to the slow cooker.
Add the frozen hash browns, condensed cheddar soup, 1 cup of the shredded cheese blend, the sour cream, and salsa to the slow cooker. Stir until the ingredients are evenly combined.
Scatter the remaining 1 cup of shredded cheese over the top.
Cover and cook on High for 3–4 hours or on Low for 4–6 hours, until the potatoes are fork-tender and the casserole is heated through.
If desired, sprinkle chopped parsley over the finished casserole for a touch of color.