Preheat the oven to 350°F. Spray a 1½ quart casserole dish with nonstick spray.
Heat the olive oil in a skillet over medium heat. Once hot, add the onion and garlic, then cook until the onion is translucent, about 5 minutes.
½ tablespoon olive oil, 1 large onion, 3 cloves garlic
Add the spinach and cook until wilted.
½ pound spinach leaves
Remove from heat and transfer to a large bowl. Add the rice, beans, chili powder, and green chiles.
2 cups cooked brown rice, 1 can (15 ounces) black beans, 1 tablespoon chili powder, 1 can (4 ounces) chopped green chiles
In a separate bowl, mix the ricotta and milk until smooth. Stir in 1 cup of mozzarella.
1 cup part-skim ricotta cheese, ¼ cup nonfat milk, 1½ cups shredded part-skim mozzarella cheese
Spread ⅓ of the rice mixture in the bottom of the dish, then half of the ricotta mixture. Repeat the layers, ending with the rice mixture.
Cover the casserole dish and bake for 30 minutes.
Uncover, spread the remaining mozzarella on top, then bake, uncovered, until the cheese melts, about 5 to 10 minutes.
1½ cups shredded part-skim mozzarella cheese