Grilled Spiced Snapper with Mango and Red Onion Salad

Name: Grilled Spiced Snapper with Mango and Red Onion Salad
Ingredients: 1 5-lb. or two 2½-lb. head-on whole fish (such as red snapper or black sea bass), cleaned; Kosher salt; ⅓ cup chaat masala, vadouvan, or tandoori spice; ⅓ cup vegetable oil, plus more for grill; 1 ripe but firm mango, peeled, cut into irregular 1½ pieces; 1 small red onion, thinly sliced, rinsed; 1 bunch cilantro, coarsely chopped (leaves and stems); 3 Tbsp. fresh lime juice; Extra-virgin olive oil (for drizzling); Lime wedges (for serving)