Prepare the slow cooker by lightly greasing it with cooking spray or oil.
Place chicken breasts in the bottom of the slow cooker.
In a medium bowl, whisk together olive oil, lemon juice, oregano, thyme, salt, and pepper.
Pour the olive oil mixture over the chicken.
Add sliced onion, bell peppers, zucchini, and garlic around and on top of the chicken.
Pour chicken broth over the vegetables and chicken.
Cover and cook on low for 4–5 hours or until chicken reaches 165°F and vegetables are tender.
Remove chicken from the slow cooker and shred or slice.
Return chicken to the slow cooker and stir to combine with the vegetables.
Sprinkle crumbled feta cheese and olives over the top before serving.
Garnish with chopped fresh parsley and serve warm.