Heat grill pan (or outdoor grill) to medium high. Meanwhile, cut zucchini on the bias in 1/2-inch-thick slices. Toss zucchini slices in medium bowl with 2 tablespoons olive oil, 1 teaspoon kosher salt, red pepper flakes and 1/2 teaspoon black pepper until well coated.
Brush grill or grill pan with olive oil to prevent sticking. Place zucchini on hot grill pan and cook 2 minutes per side, until grill marks form. Return grilled zucchini to bowl with residual olive oil and seasoning. Add 1 tablespoon red wine vinegar while zucchini is still warm. Toss to coat. Set aside.
Combine ricotta, parmesan, 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper in small bowl until well combined and smooth. Set aside.
In bowl of food processor, combine toasted walnuts, honey, remaining tablespoon red wine vinegar and remaining teaspoon salt. Pulse until chunky (similar to chunky peanut butter texture). Scrape down sides of bowl as necessary.
Heat square griddle (or large skillet) over medium heat. Spread about 1 teaspoon mayonnaise on 1 side of bread slices. Place 4 bread slices, mayonnaise-side-down, in hot skillet. If necessary, assemble sandwiches in batches. Divide ricotta cream evenly over 4 bread slices in skillet. Top each with 4 or 5 pieces of grilled zucchini, 5 basil leaves and 2 slices of mozzarella. Spread a couple spoonfuls of honey-walnut spread over. Top with remaining bread slices, mayonnaise-side-up. Grill 2 minutes; carefully flip sandwiches. Reduce heat to low and grill 5 minutes longer, until bread is golden brown and cheese is melted. Serve immediately.
- 2 small zucchini
- 4 tablespoons (1/4 cup) olive oil, divided, plus additional for grill pan
- 2 1/2 teaspoons kosher salt, divided
- 1 teaspoon red pepper flakes
- 3/4 teaspoon freshly ground black pepper, divided
- 2 tablespoons red wine vinegar, divided
- 1/2 cup (4 ounces) Wisconsin Ricotta cheese
- 1/4 cup (scant 2 ounces) Wisconsin Parmesan cheese, grated
- 3/4 cup walnut pieces, toasted
- 2 tablespoons honey
- 3-4 tablespoons mayonnaise
- 8 slices sourdough bread
- 20 large fresh basil leaves
- 8 slices Wisconsin Mozzarella cheese