Season both sides of sliced chicken breasts with salt and pepper.
Heat oil in a large skillet over medium high heat. Add chicken and cook until golden brown, cooked through and no longer pink (about 4 minutes on each side depending on thickness). Transfer chicken to a plate and set aside (leave juices in skillet).
In the same skillet, cook zucchini, bell pepper and onion until zucchini is crisp-tender (about 3 to 4 minutes), stirring frequently.
Add garlic and cook an additional 30 seconds, while stirring.
Add marinara sauce, diced tomatoes, red pepper, Italian seasoning and bay leaf. Stir to combine.
Bring to a simmer and simmer for 5 minutes, stirring occasionally (reduce heat as necessary to maintain a simmer).
Remove and discard bay leaf. Return chicken to skillet and coat with sauce mixture.
Serve sprinkled with chopped fresh parsley or basil, if desired.