Cut chicken breasts into bite-sized pieces and season with garlic powder, salt, and pepper.
Dredge the chicken pieces in flour and set aside.
Heat olive oil in a large skillet over medium-high heat.
Cook the chicken in batches for about 3 minutes per side or until golden brown, then transfer to a plate.
In the same skillet, melt butter over medium heat.
Add sliced mushrooms and chopped onions, sauté for 6 to 8 minutes until tender.
Stir in Dijon mustard, Worcestershire sauce, and minced garlic; cook for 1 minute until fragrant.
Pour in chicken broth and scrape up browned bits from the skillet bottom.
Return chicken to skillet and simmer for 2 minutes.
Lower heat and gently stir in sour cream without boiling to combine.
Adjust seasoning with salt and pepper and remove from heat.
Serve immediately with egg noodles, rice, or crusty bread.