Soak wooden skewers in water for 20 minutes. You can also use metal skewers, and those do not need to be soaked.
Preheat an outdoor grill to medium-high.
Brush grill grates with oil.
Thread the skewers with pieces of zucchini, squash, mushrooms, onions, and lemons. Set aside.
In a mixing bowl combine olive oil, garlic, thyme, and oregano; whisk until completely incorporated.
Brush the skewered veggies with the oil mixture.
Season with salt and pepper.
Transfer to preheated grill; grill for 12 to 15 minutes, or until vegetables are tender, turning skewers occasionally.
Remove from grill and transfer to a serving plate.
Garnish with parsley, squeeze a bit of lemon juice over the kebabs, and serve.