Preheat the grill to medium-high heat.
If using wooden skewers, soak them in water for about 10 minutes to prevent burning.
In a large bowl, combine the zucchini, bell pepper, cherry tomatoes, red onion, and mushrooms.
Drizzle the olive oil over the vegetables, then sprinkle with Italian seasoning, salt, and pepper. Toss to make sure all the veggies are coated.
Thread the marinated vegetables onto the skewers, alternating between the different vegetables for color and variety.
Place the skewers on the preheated grill. Cook for about 10-15 minutes, turning occasionally until the veggies are tender and slightly charred.
Remove the skewers from the grill and let them cool for a minute.
Garnish with fresh basil, if desired, and serve warm.