Heat a heavy-bottomed pot over medium heat, feeling the gentle warmth as the oil begins to shimmer.
Add the sliced mushrooms to the pot, stirring occasionally until they release their earthy aroma and turn a deep golden brown, about 8 minutes.
Push the mushrooms to one side of the pot, then add the diced chicken, seasoning with salt and pepper.
Cook the chicken until no longer pink and fully cooked through, about 6 minutes, stirring occasionally for even color.
Pour in the chicken broth, scraping the bottom of the pot to loosen any flavorful browned bits, then stir in the heavy cream.
Bring the mixture to a gentle simmer, then add a squeeze of lemon juice to brighten the flavors.
Allow the soup to simmer gently for about 15 minutes, stirring occasionally, until the flavors meld and the broth thickens slightly.
Taste and adjust seasonings with additional salt, pepper, or lemon juice as desired.
Serve the soup hot, garnished with a sprinkle of fresh herbs if desired, and enjoy the rich, smoky sweetness of the caramelized mushrooms in every spoonful.