1. Preheat broiler to high.
2. Cut the chiles in half lengthwise; discard seeds and membranes. Place chile halves, skin side up, on a foil-lined baking sheet; flatten with hand. Broil 8 minutes or until blackened. Place in a paper bag; close tightly. Let stand 10 minutes. Peel chiles. Coarsely chop chiles; place in a bowl. Add corn and onion to pan; broil 10 minutes, stirring twice. Add corn mixture to chopped chiles; stir in oregano, oil, lime juice, 1/4 teaspoon salt, cumin, and black pepper.
3. Cut tops off tomatoes; set aside. Carefully scoop out tomato pulp, leaving shells intact. Drain pulp through a sieve over a bowl, pressing with the back of a spoon to extract liquid. Reserve 1 1/4 cups liquid, and discard remaining liquid. Sprinkle tomatoes with 1/2 teaspoon salt. Invert tomatoes on a wire rack; let stand 30 minutes. Dry insides of tomatoes with a paper towel.
4. Place quinoa in a fine sieve, and place sieve in a large bowl. Cover quinoa with water. Using your hands, rub the grains together for 30 seconds; rinse and drain. Repeat the procedure twice. Drain well. Combine reserved tomato liquid, quinoa, 1/4 cup water, and the remaining salt in a medium saucepan; bring to a boil. Cover, reduce heat, and simmer for 15 minutes or until liquid is absorbed. Remove from heat; fluff with a fork. Add quinoa mixture to corn mixture; toss well.
5. Preheat oven to 350°.
6. Spoon about 3/4 cup corn mixture into each tomato. Divide cheese evenly among tomatoes. Place tomatoes and tops, if desired, on a jelly-roll pan. Bake at 350° for 15 minutes. Remove from oven. Preheat broiler. Broil the tomatoes 1 1/2 minutes or until cheese melts. Place tomato tops on tomatoes, if desired.