In a large skillet over medium-high heat, brown 1 lb lean ground beef, breaking it into crumbles as it cooks. Cook until no pink remains. If there is excess fat or liquid, drain it off (you can blot with paper towels).
In a small bowl, stir together 1 package taco seasoning mix and 1/4 cup water until combined.
Add the seasoning mixture to the cooked beef, stir to coat, and cook briefly until the liquid is mostly absorbed or thickened. Remove the skillet from the heat and let the beef cool slightly.
In the bowl of a food processor, combine 18 oz cream cheese (cut into pieces if firm), 1 cup cottage cheese, and 1 cup salsa. Process until smooth and well combined.
Spread the seasoned beef in an even layer across the bottom of a 9x13-inch glass baking pan or into individual ramekins.
Spread the cream cheese–cottage cheese–salsa mixture evenly over the beef layer.
Sprinkle 2 cups (8 oz) finely shredded medium cheddar cheese evenly over the cream cheese layer.
Top the cheese with 2 cups shredded lettuce, then 2 cups finely chopped tomatoes in an even layer.
If using, add 1 diced avocado and garnish with cilantro.
If not serving immediately, cover tightly with plastic wrap and refrigerate until ready to serve. (For best avocado color, add the diced avocado just before serving.)
Serve the dip with taco chips or firm tortillas.