Heat your large heavy-bottomed pot over medium heat until warm, then add olive oil.
Add sliced mushrooms to the pot and sauté until they release their aroma and turn a deep golden brown, about 8 minutes. Stir occasionally to prevent sticking.
Push the mushrooms to one side of the pot, then add diced chicken to the empty space. Sear the chicken until golden on all sides, about 5 minutes, stirring occasionally.
Pour in the chicken broth, scraping up any browned bits from the bottom of the pot. Bring to a gentle simmer and cook for about 10 minutes, or until the chicken is cooked through and tender.
Stir in the heavy cream, chopped thyme, and a squeeze of lemon juice. Continue cooking for another 3-4 minutes until the soup is heated through and slightly thickened.
Taste the soup and adjust seasoning if needed—adding more lemon for brightness or salt as desired.
Use a ladle to serve the hot, velvety soup into bowls, ensuring each has an even mix of chicken, mushrooms, and broth.
Finish with a final squeeze of lemon or a sprinkle of fresh thyme if desired, then enjoy this comforting, creamy mushroom chicken soup.