How to Make It
Preheat a grill to medium-high (about 450°F), or heat a grill pan over medium-high. Spray corn, okra, celery, and scallions with cooking spray; grill vegetables until slightly charred, 5 to 6 minutes. Place okra in large bowl. When cool enough to handle, cut kernels off corn, slice celery, and chop scallions; add to bowl with okra. Add basil, red pepper, oil, vinegar, 5/8 teaspoon salt, and 1/4 teaspoon black pepper; toss to combine.
Sprinkle both sides of snapper with remaining 1/2 teaspoon salt and remaining 1/4 teaspoon black pepper. Coat grill grates and fish with cooking spray. Carefully place fish, skin side down, on oiled grates, and grill 5 to 6 minutes. Carefully flip, and grill until cooked through, 4 to 5 more minutes.
Divide grilled vegetable mixture among 4 plates; top with fish.