Rinse beef brisket and pat dry.
Grind both salt and pepper over both sides of the meat.
Heat a skillet over medium high heat and add one tablespoon of olive oil.
Once the oil is hot, sear the brisket on both sides until golden brown, about two minutes per side.
In a separate pan, heat over medium heat and add remaining tablespoon of olive oil.
Saute onions until golden brown.
Add brisket, fatty side down into your slow cooker or Instant Pot.
On top of the brisket, place the cooked onion, minced garlic, tomatoes, stock and add a bit more salt and pepper.
Cook on the slow cook setting in your Instant Pot for 6 hours.
Cooking the meat for 6 hours will allow you to slice it for a nice presentation. If you like your meat more tender so that it falls apart, cook for 8 hours total.