- 2½ tablespoons olive oil, divided, plus more for the grill
- 1 large zucchini, thinly sliced
- 1 large yellow squash, thinly sliced
- 1½ teaspoons kosher salt, divided
- ½ teaspoon black pepper, divided
- 1 large tomato, thinly sliced
- Lemon Aïoli (see below)
- 1 focaccia bread loaf, halved lengthwise
- 3 (1-oz.) low-moisture mozzarella cheese slices
- Preheat grill to low. Brush the grill grates with oil. Toss the zucchini and squash with 1 teaspoon of the salt, ¼ teaspoon of the pepper, and 2 tablespoons of the oil in a colander. Press to drain any moisture. Sprinkle the tomato with the remaining salt, pepper, and oil.
- Spread 4 tablespoons Lemon Aïoli on the cut sides of the bread halves. Place the mozzarella in a single layer on the bottom half. Layer the zucchini, squash, and tomato over the cheese. Cover with the top half of the bread and lightly press.
- Grill the sandwich, covered, until the cheese is melted, the filling is warm, and the bread is toasted, about 10 minutes, turning halfway through. Cut into quarters and serve.
Stir together 1 cup mayonnaise, 2 tablespoons Dijon mustard, and ¼ cup fresh lemon juice. Other uses: Serve with smoked salmon, spread on avocado toast, or mix into deviled-egg filling.