Prepare barley according to package directions; drain.
Heat oil in a large nonstick skillet over medium-high. Add mushrooms; cook, stirring often, until browned, 7 to 8 minutes. Add cumin; cook, stirring constantly, 1 minute. Add salt, garlic, shallot, and poblano, and cook, stirring often, until poblano is softened slightly, 3 to 4 minutes. Stir in barley and stock. Bring to a simmer; cook until absorbed, 2 to 3 minutes.
Stir together sour cream and lime juice. Spoon mushroom mixture into 4 bowls, and top servings with sour cream mixture and scallions. Sprinkle with paprika, if desired.