Season zucchini with salt and pepper. Heat a grill pan over medium-high heat.
Spray with oil and add the zucchini, grill on each side about 2 minutes each, until grill marks form. Set aside.
Spray one side of each slice of bread.
Heat a large non-stick skillet over medium-low heat. Place 2 slices of bread oiled side down on the skillet.
Top each piece of bread with 1 ounce of cheese, divide the zucchini on top, grilled chicken, tomato slices and basil and the remaining cheese.
Top with the remaining bread oil side up. Use a heavy pot or skillet to press it down and cook until the bottom piece of bread is golden, about 4 to 5 minutes.
Use a spatula to carefully flip the sandwich over. Cook until the other slice of bread is golden brown, about 3 to 4 minutes.
Cut in half diagonally and serve with your favorite soup.