Preheat oven to 375°.
Melt the butter in a medium nonstick skillet over medium-high heat. Add the chopped onion and minced garlic, and sauté 5 minutes. Remove from heat, and stir in ground cumin and salt. Combine onion mixture, rice, and egg substitute in a bowl. Combine tomatoes and tomato sauce in a bowl. Combine the cheeses in a small bowl. Spread 1 1/4 cups tomato mixture in bottom of a 13 x 9-inch baking dish, and top with 1 1/2 cups rice mixture. Arrange half of green chiles on top of rice mixture, and sprinkle with half of cheese mixture. Repeat the procedure with the remaining tomato mixture, rice mixture, and chiles. Bake, uncovered, at 375° for 30 minutes. Sprinkle top with remaining cheese mixture, and bake an additional 5 minutes or until the cheese is melted. Garnish with oregano sprigs, if desired.