Preheat a barbecue to medium-high heat. Slice the eggplant, fennel and zucchini lengthways into 1 cm-thick pieces. Sprinkle with half the salt. Coat with cooking spray.
Barbecue capsicum, skin side down, until the skin is blackened and blistered, 3 to 4 minutes. Cook eggplant, fennel and zucchini on one side until grill marks are dark brown but vegetables are still very firm, about 4 minutes. Turn over and barbecue until browned and just tender, about 3 minutes for zucchini and 5 to 6 minutes longer for eggplant and fennel.
Coat cut sides of tomatoes with cooking spray. Barbecue, cut sides down, just until light grill marks appear, 3 minutes.
Heat the oil in a small frying pan over medium heat. Add garlic, marjoram and remaining salt. Sauté 1 minute.
Peel grilled capsicum and cut into thin strips. Cut the rest of the vegetables into bite-sized chunks. Transfer to a medium bowl. Add olive oil mixture and vinegar. Toss to coat. Serve at room temperature.