Transfer liquid from pot roast package to a large skillet; add mushrooms and picante sauce. Cut pot roast into 1- to 1-1/2-inch cubes; add to skillet. Bring to boiling; reduce heat. Cover and simmer for 10 minutes.
Meanwhile, in a medium saucepan bring chicken broth to boiling; stir in couscous. Remove from heat. Cover and let stand 5 minutes. Fluff with a fork; stir in snipped cilantro.
Spoon pot roast mixture on top of hot cooked couscous mixture. Serve with sour cream, tomato, and/or avocado and top with cilantro sprigs. Makes 4 to 6 servings.