Season the cube steak on both sides with sea salt and black pepper.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Place the steak in the skillet and sear for 3-4 minutes per side until a deep golden crust forms and it reaches your desired doneness.
Remove the steak from the pan and set aside on a plate to rest.
In the same skillet, add the sliced mushrooms and diced onion, sautéing for 5 minutes until the vegetables are softened and browned.
Stir in the minced garlic and fresh thyme, cooking for 1 minute until fragrant.
In a small bowl, whisk the beef bone broth and arrowroot starch together until no lumps remain.
Pour the broth mixture into the skillet, scraping the bottom of the pan to release the flavorful browned bits.
Simmer the sauce for 2-3 minutes until it thickens into a glossy gravy.
Return the steak to the pan to coat with the gravy before serving immediately.