Place roast in large roaster pan.
Combine next 6 ingredients; sprinkle over roast.
Place onions around roast.
Pour water in pan.
Bake tightly covered, at 350* for about 3-1/2 hours until roast is almost tender.
Add more water if needed.
Add carrots and potatoes; bake for 1-1/2 hour more, until vegetables are tender.
Baste roast and vegetables with juices.
Thicken with flour and water mix if desired.