cheesy broccoli and rice casserole

Ingredients

• 2 (6.4 oz) boxes creamy four cheese rice a roni
• 1 large onion,chopped
• 2 cloves garlic,minced
• 2 cups fresh or frozen broccoli flowerettes,cooked until tender
• 1 (7 oz.) jar sliced mushrooms,drained
• 1 (8 oz.) can water chestnuts,chopped
• 2 cans cream of celery or mushroom soup
• 1-2 cup cheddar or monterey jack cheese,depending on how cheesy you want it
• 2 tablespoons chopped fresh parsley
• 1/2 teaspoon freshly ground black pepper
• - salt to taste
• 1/2 cup chicken stock or broth;more if needed