Place beef brisket, fat side down in Crock pot. Sprinkle brisket with onion, salt, pepper and garlic powder. Pour chili sauce over brisket. Set Crock Pot on low for 6 hours. Pour beer over brisket.
Increase temperature to high and continue cooking for 30 minutes. Place brisket on large serving platter. Slice brisket very thin and serve with hot cooking liquid. Garnish with sliced tomatoes and parsley.