Heat a heavy-bottomed pot over medium heat, feeling the warmth as the oil begins to shimmer.
Add sliced mushrooms to the pot, spreading them out evenly. Sauté for about 8 minutes, stirring occasionally, until they release their earthy aroma and turn a deep golden brown.
Push the mushrooms to one side of the pot, then add diced chicken to the empty space. Season with salt and pepper, and cook for about 6 minutes until the chicken is no longer pink and begins to brown slightly.
Pour in the chicken broth, scraping up any browned bits from the bottom of the pot to build flavor. Bring the mixture to a gentle simmer.
Stir in the cream and squeeze in the lemon juice, then reduce the heat to low. Let the soup simmer gently for about 15 minutes, stirring occasionally, until flavors meld and the soup thickens slightly.
Taste the soup and adjust seasoning with more salt or pepper if needed. Serve hot, garnished with a sprinkle of fresh herbs if desired.