Preheat the oven to 220°C / 425°F and line a baking tray with parchment paper.
Slice the cabbage very thinly, rinse it if needed, then dry it well so it sautés instead of steaming.
Warm 30 ml / 2 tbsp olive oil in a large pan over medium-low heat. Add the garlic clove and cook for about 1 minute without browning it.
Add the cabbage and salt. Toss well and cook for 8–10 minutes, stirring often, until softened but still lightly textured.
Add the red wine vinegar, black pepper, and chili flakes if using. Cook for 1 minute, then remove and discard the garlic.
Brush the bread slices lightly with olive oil and toast them in the oven for 5–6 minutes, turning once, until crisp and pale golden.
Slice or coarsely grate the caciocavallo so it melts evenly over the hot crostini.
Spoon the warm cabbage onto the toasted bread, keeping the topping generous but not too wet.
Add the caciocavallo on top and return the crostini to the oven for 3–5 minutes, until the cheese is melted and lightly golden.
Finish with lemon zest, parsley, and a small drizzle of olive oil. Serve immediately while the bread is crisp and the cheese is warm.