Prepare the brown rice according to package instructions if not already cooked.
Season the chicken breast evenly with half of the sea salt and black pepper.
Heat the olive oil in a medium skillet over medium-high heat.
Sear the chicken for 5-6 minutes per side until golden brown and cooked through, then remove from the pan and set aside.
In the same skillet, add the diced yellow onion and sliced cremini mushrooms, sautéing until the mushrooms are tender and browned.
Stir in the minced garlic and fresh thyme, cooking for 1 minute until fragrant.
Pour in the chicken broth to deglaze the pan, using a wooden spoon to scrape up any flavorful browned bits.
Reduce the heat to low and stir in the Greek yogurt and remaining salt and pepper to create a light, creamy sauce.
Slice the cooked chicken and return it to the skillet, tossing gently to coat in the mushroom mixture.
Serve the chicken and mushrooms immediately over the warm bed of brown rice.