Prepare the chicken breasts by seasoning them with salt and pepper.
Heat olive oil in a large skillet over medium heat.
Brown the chicken breasts for approximately 5-7 minutes on each side until golden.
Remove the chicken from the skillet and set aside, lowering the heat.
Add diced onions to the same skillet and sauté until translucent, about 3-4 minutes.
Stir in minced garlic and cook for another minute until fragrant.
Add sliced mushrooms and thyme, cooking until mushrooms are browned and tender.
Pour in the chicken broth, stirring to deglaze the pan and lift any flavorful bits stuck to the bottom.
Reduce the heat and add heavy cream, stirring until well combined.
Return the chicken to the skillet, ensuring it's coated in the sauce, and cook for an additional 5 minutes.
Taste the sauce and adjust seasoning with salt and pepper if necessary.
Garnish with fresh parsley before serving.