Cut the squash into 1/2 inch slices, the bell peppers into strips, slice the zucchini and remove the stems from the mushrooms. Chop the basil and set aside.
In a medium bowl, whisk together olive oil, lemon juice, basil and garlic. Pour the marinade into a large ziplock bag and add the veggies. Seal let marinate in the refrigerator at least 1 hour.
Preheat an outdoor grill for high heat.
Place vegetables directly on the grill or skewer them and place on grill. Cook for 2 to 3 minutes per side, brushing frequently with the marinade.