Combine 3/4 cup of the Italian dressing with the chicken breasts in a zip-top bag or shallow dish. Refrigerate for at least 30 minutes, then remove the chicken and pat each piece dry with paper towels.

Heat the 2 tbsp olive oil in a large skillet over medium-high heat until shimmering. Sear the chicken for 5 to 6 minutes per side, until golden brown and the internal temperature reads 165°F (74°C). Transfer to a plate and tent loosely with foil.

In the same skillet over medium heat, cook the 3 cloves minced garlic for 60 seconds. Add the 1/2 cup chicken broth, scraping up the browned bits, then stir in the remaining 1/4 cup dressing, 1 tsp Italian seasoning, 1/2 tsp black pepper, and 1/4 tsp red pepper flakes. Simmer for 3 to 4 minutes until slightly reduced.

Remove the pan from the heat. Stir in the 2 tbsp butter and 1 tbsp lemon juice until the sauce is glossy. Return the chicken to the pan, spoon the sauce over each piece, transfer to a platter, and garnish with fresh parsley.