Grilled Halloumi Salad with Radicchio

Name: Grilled Halloumi Salad with Radicchio
Ingredients: 1/2 cup olive oil, plus more for the grill and halloumi; 1/4 cup whole-grain mustard; 2 tablespoons honey; 2 tablespoons apple cider vinegar; 2 heads radicchio (8 to 9 ounces each), quartered through the core; Kosher salt; Freshly ground black pepper; 1 medium lemon, halved; 1 (8.8-oz) package halloumi cheese, sliced into 1/2-inch thick slabs; 2 medium oranges or blood oranges, peeled and sliced into 1/2-inch thick rounds; 2 tablespoons roasted pistachios, coarsely chopped