First, add the salt pepper and oregano all over the brisket on both sides.
Next add 1/2 the onion, 1/2 carrots, 1 packet onion soup mix, a pinch or salt, and a pinch of pepper to bottom of the slow cooker. Mix together to combine.
Now place the brisket onto the onion and pour second packet of onion soup mix on both sides of the brisket.
Next top the brisket with the remaining onion, remaining carrots, mushrooms, and pinch salt and pepper on top of the brisket.
Now, cover and cook for 6 hours on low.
Finally, cover with tin foil and let rest 20 minutes so juices stay in the meat. Then cut against the grain (opposite of the meat strands going).
Top with parsley and enjoy!