Grilled Giardiniera Salad

Name: Grilled Giardiniera Salad
Ingredients: Vegetable oil, for oiling the grill grates; 2 cups white wine vinegar; 3 tablespoons kosher salt; 1 tablespoon sugar; 1 teaspoon dried oregano; 1 teaspoon whole peppercorns; 4 cloves garlic, smashed; 3 cups mini rainbow peppers; 4 medium carrots, peeled; 4 serrano peppers; 1 small head cauliflower, cut into 1-inch-thick steaks; 2 stalks celery, leaves reserved; 3/4 cup olive oil; 1 tablespoon Dijonmustard; 1 cup ricotta salata, grated; 1 cup pitted black olives, halved; Grilled Italian sausage and hoagie rolls for serving, optional