In a large bowl, whisk together the olive oil, minced garlic, lemon juice, oregano, thyme, salt, and black pepper.
Add the chicken breasts to the marinade, making sure they are well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Preheat the grill to medium-high heat.
While the grill is heating, toss the sliced bell peppers, zucchini, and red onion in the remaining marinade.
Remove the chicken from the marinade and place it on the grill. Cook for about 6-7 minutes on each side, or until the internal temperature reaches 165°F.
In the last 5 minutes of cooking, add the vegetables to the grill. Cook until they are tender and slightly charred, about 5-7 minutes.
Remove the chicken and veggies from the grill and let the chicken rest for 5 minutes before slicing. Serve warm.