In a large bowl, combine rice, salsa and oregano. In a second bowl, combine refried beans, corn, chile powder and cumin.
Coat a 12 x 8 x 2-inch baking dish with nonstick cooking spray. Spread half of the rice mixture evenly in dish. Layer refried bean mixture and half the cheese over the rice. Scatter spinach over cheese. Top with remaining rice mixture and cheese.
Cover with plastic wrap and refrigerate for up to 2 days.
Heat oven to 350 degrees F. Bake, uncovered, for 35 minutes or until internal temperature registers 140 degrees F. Sprinkle with cilantro before serving.