Step 1Place rice in steamer with 1 1/4 cups water. Cover and steam until rice is tender and water absorbed, 55 minutes to 1 hour. (Or place rice in saucepan with 2 cups water, bring to boil, cover and simmer over low heat until rice is tender, about 45 minutes.)
Step 2Combine lentils and 2 cups water in saucepan. Heat to boiling, reduce heat and simmer until lentils are tender, 30 to 35 minutes. Add more water toward end of cooking, if necessary. Drain and set aside.
Step 3Saute onion and garlic in skillet sprayed with nonstick cooking spray over medium-low heat until tender, 2 to 3 minutes. Stir in carrots and 1/2 cup water. Bring to simmer, cover, and cook until carrots are just tender, about 5 minutes. Stir in mushrooms. Cook and stir about 1 minute.
Step 4Combine rice and lentils in serving bowl. Stir in onion mixture, then tomato, green onions, lemon juice and cilantro. Season with salt.