Pat the chicken breasts dry and, if thick, slice them horizontally or pound them to an even thickness.
Season both sides of the chicken with paprika, Italian seasoning, garlic powder, salt, and black pepper.
Heat olive oil in a large skillet over medium-high heat.
Add the chicken and cook for 4–5 minutes per side, or until golden and cooked through.
Transfer the chicken to a plate and loosely cover with foil.
Add 1 tablespoon butter to the same skillet.
Add the onion and carrots and cook for about 3 minutes.
Add the broccoli and bell pepper and cook for another 3–4 minutes.
Add the zucchini and minced garlic and cook for approximately 2 minutes.
Season the vegetables with Italian seasoning, salt, and black pepper.
Reduce the heat to medium.
Add chicken broth, 2 tablespoons butter, Dijon mustard, lemon juice, paprika, and Italian seasoning.
Stir and scrape the browned bits from the bottom of the skillet.
Simmer the sauce for 2–3 minutes.
Return the chicken to the skillet.
Spoon the sauce and vegetables over the chicken.
Simmer for another 2–3 minutes so the flavors combine.
Make sure the chicken reaches an internal temperature of 165°F (74°C).
Sprinkle with fresh parsley and an additional squeeze of lemon juice if desired.
Serve warm.