Preheat oven to 375º. Cook the ground beef in a 10-inch skillet over medium heat, stirring frequently, until browned and crumbly, about 5 minutes. Drain. Reduce heat to low. Stir in the frozen pepper stir-fry, 1/2 cup water and the taco seasoning. Simmer for 5 minutes longer.
Meanwhile, unroll the crescent roll dough. Line the bottom and sides of an ungreased 9-inch square baking dish with the dough, pressing together to form the crust. Bake until lightly browned, about 5 minutes.
Remove the crust from the oven and immediately sprinkle the bottom with 1 cup crushed tortilla chips. Spoon the ground beef mixture over the tortilla chips, stopping 1 inch from each side. Spread the sour cream evenly over the beef mixture. Cover with the cheddar. Top with the remaining chips.
Bake until the crust is golden brown and cheese is melted, 15-20 minutes. Cut into squares. serve immediately with the lettuce and tomatoes, if desired.