In a small bowl, whisk together the canola oil, vinegar, sugar, grated onion, poppy seeds, mustard and salt. Set aside until ready to use.

Put the zucchini, yellow pepper and tomatoes in a bowl and toss with olive oil, salt and black pepper. Place the vegetables onto skewers or arrange in a grill basket. Grill over medium-high heat for 10-12 minutes until crisp-tender.

Transfer vegetables to a serving bowl. Season with basil, parsley and thyme. Toss with the dressing and serve.