Preheat the oven to 350°F (175°C).
In a large skillet over medium-high heat, cook 1 pound ground beef until no longer pink, breaking it up with a spoon; drain any excess grease.
Add 3/4 cup water and 1 envelope taco seasoning to the skillet, bring to a boil, then reduce heat to low.
Stir in 4 ounces cream cheese, simmer for about 5 minutes until the cream cheese is melted and the mixture is smooth; remove from heat and transfer to a bowl to cool slightly.
Cook 12 jumbo pasta shells according to package directions until al dente; drain and toss with 2 tablespoons melted butter to prevent sticking.
Spoon 1/2 cup salsa into the bottom of an 11x7 baking dish and spread into a thin layer.
Fill each buttered shell with a scoop of the beef and cream cheese mixture and place the filled shells open-side up in the prepared baking dish.
Drizzle 1/2 cup green enchilada sauce evenly over the filled shells.
Bake uncovered for 20 minutes, then remove from oven and sprinkle 1 cup shredded Colby Jack cheese over the shells.
Return to the oven and bake an additional 10–15 minutes, until the cheese is melted and bubbly.
Before serving, top the shells with 1/2 cup crushed Fritos and dollops of 1/2 cup sour cream.