1. Heat grill to medium-high heat.
2. Combine oil, basil, marjoram, and salt in a mixing bowl; reserve 1 tablespoon of mixture in a small dish; set aside.
3. Coat all vegetables with cooking spray (spray both sides); grill vegetables, turning once halfway through cooking until charred in spots. Tomatoes and onion will take ~3 minutes, zucchini and eggplant ~4 minutes, and bell pepper ~ 5 minutes in total to cook until desired doneness.
4. Rub tablespoon on reserved oil/spice mixture onto chicken and sprinkle with black pepper.
5. Grill the chicken 4-5 minutes per side, until no longer pink in the center or until internal temperature reaches 160 degrees.
6. Transfer the grilled vegetables to a cutting board, slicing into 1” pieces; toss cut vegetables with oil/herb mixture. Serve chicken and herbed vegetables together.