Preheat oven to 425 degrees
Dice sweet potato and toss with 1/8 cup olive oil, 1/4 teaspoon salt, 1/4 teaspoon pepper, and 1/4 teaspoon onion powder
Spread sweet potatoes out into one layer on a baking sheet
Roast at 425 for 15 minutes, then stir
Roast an additional 10-15 minutes, until fork tender
Cook brown rice according to package instructions (I used a rice cooker for convenience)
In a skillet, sauté mushrooms and garlic with 1 teaspoon of olive oil
Cook on medium high for around 10 minutes, or until mushrooms emit their liquid and start to cook down
Add frozen spinach and cover with a lid, until spinach thaws and breaks apart
In a large mixing bowl, combine mushroom mixture, brown rice, sweet potatoes, greek yogurt, parsley, cheddar cheese, and parmesan cheese
Salt to taste (I added 1 teaspoon of salt)
Transfer mixture to a 13 X 9 casserole dish
Top with mozzarella cheese
Bake at 400 degrees for 20-25 minutes, or until cheese is bubbly and beginning to brown