Cut the chicken breasts into 1-inch pieces and season generously with garlic powder, salt, and pepper. Dredge each piece in flour and set aside.

In a large skillet, heat olive oil over medium-high heat and add the seasoned chicken pieces, cooking for about 3 minutes per side until golden brown and cooked through.

Remove the chicken and set aside on a plate.

Lower heat and add butter and a drizzle of olive oil, then add cremini mushrooms and diced onion, sautéing for about 6 to 8 minutes.

Stir in Dijon mustard, Worcestershire sauce, and garlic powder, cooking for an additional minute.

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

Reduce heat to low and stir in sour cream until smooth. Heat through without boiling, taste, and adjust seasoning if necessary.