Heat a large heavy-bottomed pot over medium heat and add a splash of oil. When shimmering, add the diced onion and sauté until translucent and fragrant, about 5 minutes.
Add sliced mushrooms to the pot and cook, stirring occasionally, until they release their juices and turn golden brown, about 8 minutes. This develops their earthy flavor and juicy texture.
Push the mushrooms to the sides of the pot and add minced garlic to the center. Cook for about 30 seconds until fragrant, stirring constantly to prevent burning.
Pour in the chicken stock and bring the mixture to a gentle simmer. Let it bubble softly for 10 minutes to meld the flavors.
Stir in the shredded cooked chicken and add the heavy cream, stirring until well combined. Continue simmering for another 5 minutes to heat through and thicken slightly.
Taste the soup and season with salt and pepper as needed. If the soup feels too thick, thin it with a little more stock until you reach your desired consistency.
Squeeze fresh lemon juice into the soup to add a bright, zesty note, and sprinkle with chopped herbs for a fresh finish.
Give the soup a final stir and ladle it into bowls. Serve hot, garnished with extra herbs if desired, and enjoy the comforting, creamy texture with a hint of earthiness and brightness.
