Grease a 9x13 baking dish and preheat oven to 375 degrees, then heat olive oil in a large skillet over medium-high heat until shimmering and swirl to coat pan. Slice chicken breasts in half lengthwise to create thinner pieces, then season chicken generously on both sides with seasoned salt and pepper. Brown chicken in olive oil over medium-high heat for about three minutes a side, then remove and place in prepared baking dish.
Reduce heat to medium and add butter to the same skillet. When butter is melted, swirl to coat, then saute onion in butter over medium heat for four minutes until slightly browned and softened. Add mushrooms, garlic, sea salt, thyme, parsley, and oregano to pan and saute about another eight minutes until mushrooms are browned and softened, stirring occasionally. Stir in broth, scraping up any browned bits from the bottom of the pan, and saute another minute.
Pour mushroom mixture over chicken and bake at 375 degrees for 20-25 minutes, or until chicken is cooked through to 160 degrees. Top evenly with mozzarella, return to oven, and broil on high for another 5 minutes until cheese is browned. Serve chicken and mushrooms over pasta or rice (or eat alone or over veggie "noodles" to keep it low carb).
Notes
If your chicken is on the thinner side, reduce cooking time accordingly. This dish is also very juicy, so if you'd like to create a thicker sauce just remove the chicken, mushrooms, and onions from the baking dish when done and whisk a little flour or cornstarch in with the pan juices to thicken them up. I topped mine with some fresh chopped parsley from my garden for extra flavor + contrast, but this is optional.