01 -
Preheat the oven to 400 °F. Pat chicken breasts dry and season both sides with half of the salt and pepper. Pound breasts to an even thickness of ¾ inch if needed for uniform cooking.
02 -
Heat 1 tablespoon of olive oil in a large oven-safe skillet over medium-high heat until shimmering. Sear chicken breasts for 2 to 3 minutes per side until golden brown. Remove and set aside.
03 -
Add remaining olive oil to skillet, reduce heat to medium. Sauté diced onion with a pinch of salt for 3 to 4 minutes until translucent. Stir in sliced mushrooms and cook for 6 to 8 minutes until moisture evaporates and edges brown.
04 -
Stir in minced garlic and cook for 30 seconds until fragrant. Add spinach and toss for 1 to 2 minutes until just wilted. Mix in dried Italian herbs, chicken bouillon powder, remaining salt and pepper, then deglaze skillet with chicken broth, scraping browned bits. Simmer for 1 to 2 minutes to develop flavors.
05 -
Nestle seared chicken back into the skillet with accumulated juices. Spoon mushroom and spinach mixture over the top. If not using skillet, transfer contents to a 9 x 13 inch baking dish and spread evenly.
06 -
Bake at 400 °F until chicken reaches 165 °F internal temperature, about 15 to 20 minutes depending on thickness. Optionally broil for 1 to 2 minutes for additional browning, monitoring closely.
07 -
Allow chicken to rest for 5 minutes to retain juices. Adjust seasoning of pan sauce as needed, then spoon sauce over chicken before serving.