Take a bowl and whisk together olive oil, balsamic vinegar, soy sauce, salt, sugar, garlic powder, black ground pepper, and herbs de provence seasoning. Set aside. Chop all of your vegetables into 1/2 slices (zucchinis, onions, green pepper, yellow pepper, and red pepper).
Take 2 ziplock bags, and in one bag add zucchinis, green peppers, yellow peppers, and red peppers. In your second ziplock bag, add the chopped onions. (The onions are separate since they cook faster upon grilling, and will not cook at the same rate as the peppers & zucchinis). In the first ziplock bag containing the zucchinis and peppers, pour 2/3 of your oil and balsamic mixture. In the second ziplock bag containing the onions, pour the rest of your oil and balsamic vinegar marinade. Allow vegetables to marinate for at least 1 hour prior to grilling.
Preheat grill until it reaches medium heat. Brush a bit of olive oil onto a nonstick grilling skillet, and grill the onions until tender. Remove onions from heat and place these in clean bowl. Next grill the zucchinis and peppers until tender. Once cooked remove from heat, and add these to your clean bowl as well.
Cut a fresh lemon and squeeze the lemon juice onto your cooked vegetables. Pour the left over marinade into your bowl with the grilled vegetables, toss, serve, and enjoy!