Preheat oven to 425°F. Cook yellow rice according to package directions in large saucepan. Cut off tops of bell peppers and remove any ribs and seeds. Set upright in 2-quart microwave baking dish, trimming bottoms just enough so that they sit level. Microwave for 5 minutes at full power, or until peppers begin to soften. Let cool.
Meanwhile, heat oil in large skillet over medium heat. Cook crumbles for 5 minutes, stirring, until browned. Stir in scallions and cumin; remove from heat. Stir mixture into cooked rice, along with corn, olives, brine and 1½ cups cheese.
Spoon mixture into cooled peppers in dish. Pour tomato sauce into dish around peppers and cover with foil. Bake until heated through, 30 to 40 minutes. Uncover and sprinkle with remaining cheese. Tent with foil and bake until cheese is melted, about 5 minutes. Garnish with sliced scallions and serve with tomato sauce from baking dish