Slow Cooker Chicken, Broccoli and Rice Casserole

small onion, chopped

long grain brown rice (not quick-cooking or instant), rinsed and drained

boneless, skinless chicken breasts

garlic powder

dried thyme

salt

pepper

(one 14.5 ounce can) low sodium chicken broth

water (or omit the water and use a total of 2¾ cups chicken broth)

broccoli, cut into small pieces (4-5 cups)

plain Greek yogurt

grated Parmesan cheese

grated cheddar cheese