Thaw shrimp according to package instructions; reserve in refrigerator until ready to use.
Heat oil in a large skillet over medium heat. Add onion, garlic, salt, pepper, saffron and hot pepper flakes. Cook until golden, about 5 min. Stir in rice until grains are shiny and coated. Pour in tomato juice, broth and lemon juice; bring to a boil. Cover; reduce heat and simmer 15 min. Increase heat to medium and stir in corn and green pepper. Cover and cook 5 min. Stir in shrimp and cook, covered, until heated through, about 2 min. Let stand 5 min. before serving. Squeeze lemon juice over rice and sprinkle with green onions to garnish.