Begin by cutting chicken breasts into 1-inch pieces and seasoning them with garlic powder, salt, and black pepper. Lightly coat the chicken pieces in flour.

Heat a deep skillet over medium-high heat and add olive oil. Once shimmering, add chicken in batches and cook for about 3 minutes per side until golden brown.

In the same skillet, reduce heat, add butter and additional olive oil, then add mushrooms and onion. Sauté for 6–8 minutes until mushrooms are golden and onion is translucent.

Stir in Dijon mustard and Worcestershire sauce, allowing to cook for an additional minute.

Pour in chicken broth, scraping up browned bits, then return chicken to the skillet and simmer for 2 minutes.

Reduce heat to low, gently fold in sour cream, and warm for 1–2 minutes; adjust seasoning with salt and pepper.