Lightly season beef with kosher salt on all sides. Set InstantPot to Sautee and add oil.
Brown beef 4 minutes each side. Remove and set aside.
Add sliced onions to pot and use a wooden spoon to scrape up any browned bits. Add 1/4 cup water, if needed, to prevent burning. Saute onions until slightly softened - 3-4 minutes.
Add beef back to pot (with any juices) and pour in entire bottle of sauce. Stir to combine and coat all beef pieces.
Seal lid and set InstantPot to cook on high pressure for 30 minutes. Allow for natural release.
When pressure is released, carefully open InstantPot and remove beef chunks. Set InstantPot to sautee and add sliced peppers. Cook peppers in sauce, stirring occasionally for 5-8 minutes or until peppers are softened and sauce has reduced a bit. While peppers cook, shred beef with two forks and add beef back to pot.
Serve on a bed of rice with avocado slices and garnish with cilantro.