Split pita crosswise so you have 2 circular pieces Butter outsides of both pieces. Spread hummus on unbuttered side of both pieces. Place 1 circular half hummus-side-up on panini grill. Top with grilled vegetables, spinach and queso fresco. Carefully cover with remaining pita half, hummus-side down, and press (or grill) until sandwich is heated through. Cut in halves or quarters to serve.