Heat olive oil in a large skillet over medium-high heat.
Add chicken pieces, season with salt, pepper, and Italian seasoning, and cook until browned and cooked through, about 6-8 minutes.
Remove chicken from the skillet and set aside.
In the same skillet, add bell peppers, zucchini, squash, onion, and garlic. Sauté until vegetables are tender-crisp, about 5 minutes.
Return chicken to the skillet and stir to combine with vegetables.
Garnish with fresh parsley before serving.