Method:
In a large bowl, toss 3 tablespoons of the oil, 1 teaspoon granulated garlic, 1 teaspoon onion powder, salt and pepper together. Add mushrooms, squash and zucchini, toss well and set aside to let marinate.
Meanwhile, marinate chicken in a wide, shallow dish with remaining 2 tablespoons oil, 1 teaspoon granulated garlic and 1 teaspoon onion powder. Season with salt and pepper.
Preheat grill. Grill vegetables, flipping once, until tender and golden brown, about 10 minutes total. Transfer to a serving platter and keep warm. Grill chicken, flipping once, until just cooked through and deep golden brown, 15 to 20 minutes.
Toss spinach and dressing together in a large bowl, then transfer to plates. Arrange rice on plates and top with grilled vegetables and chicken. Serve immediately.