Step 1Place brown rice, broth and soy sauce in 4- or 5-quart pot with lid. Bring to boil over high heat. Watch carefully; turn heat to low as soon as broth boils. Cook 10 minutes, then add white rice. Stir rice, cover pot and cook 15 minutes. It usually takes 15 to 20 minutes for rice to cook. Test for doneness by scooping a few grains of rice out of pot with spoon and taste. If tender, rice is done.
Step 2While rice cooks, peel onion and cut off stem top and root bottom. Cut onion in half from stem top down. Place each half onion flat side down on cutting board and cut into 1/4-inch slices horizontally. Cut into 1/4-inch slices vertically then cut into 1/4-inch pieces crosswise. Set aside. Cut coarse green tops from green onions, leaving a little green. Holding onions together, cut off roots, then cut green onions into small pieces; set aside. Cut stems off peppers, then cut each pepper in half lengthwise. Cut out white veins and seeds and discard. Cut each pepper half into 1/4-inch strips. Hold bundle of strips together and cut crosswise into small pieces. Add to onion pile. Trim leaves from celery tops. Slice each celery rib lengthwise from top to bottom in 1/4-inch strips. Holding strips together, chop into small pieces crosswise. Add to prepared vegetables.
Step 3Put rice vinegar and olive oil in small bowl or jar with lid and stir briskly to blend.
Step 4Using fork, stir together brown and white rice in large mixing bowl. Mix fresh vegetables into rice. Add vinegar mixture and salt and pepper to taste. Using a fork and large spoon, toss and mix everything together. Taste and add more salt and pepper if needed. Serve with lemon wedges.