Pat chicken breasts dry and pound to even 3/4-inch thickness if needed. Season both sides with salt, pepper, and garlic powder.
Heat stainless steel skillet over medium-high heat. Add olive oil and heat until shimmering (about 350°F).
Place chicken in the pan and sear undisturbed for 5-6 minutes until golden brown. Flip and cook 5-6 minutes more until internal temperature reaches 160°F. Remove to a plate and tent with foil.
Reduce heat to medium. Add shallots to the same pan and cook for 2 minutes until translucent, scraping up browned bits. Add garlic and cook 30 seconds until fragrant.
Pour in white wine and increase heat to medium-high. Allow to bubble vigorously while scraping the pan. Reduce wine by half (3-4 minutes).
Add chicken stock, lemon juice, Dijon mustard, thyme, and bay leaf. Stir to combine and bring to a simmer. Reduce sauce by half until slightly thickened (4-5 minutes).
Reduce heat to low and remove thyme and bay leaf. Add cold butter cubes one at a time, whisking constantly to emulsify. Once incorporated, stir in half the parsley and adjust seasoning.
Return chicken and accumulated juices to the pan, turning to coat in sauce. Spoon additional sauce over chicken, garnish with remaining parsley, and serve immediately.