How to Make It
Open bottom vent of a charcoal grill completely. Light 2 charcoal chimney starters filled with briquettes. When briquettes are covered with gray ash, pour onto bottom grate of grill. Adjust vents as needed to maintain an internal temperature of 400°F to 450°F.
Stir together curry powder, 2 teaspoons salt, ground ginger, and garam masala in a small bowl. Place corn, red onion, and cauliflower on a large rimmed baking sheet. Sprinkle with 2 teaspoons curry mixture, and drizzle with 1 tablespoon oil; toss to coat. Place okra and squash in a large bowl. Sprinkle with remaining curry mixture, and drizzle with 1 tablespoon oil; toss to coat.
Working in batches, place corn, onion, and cauliflower mixture in a single layer on oiled grill grate. Grill, covered, until crisp-tender and lightly charred, about 4 minutes per side. Remove from grill.
Place okra and squash on oiled grate; grill, covered, until slightly charred and crisp-tender, 1 to 2 minutes per side. Place in a large bowl. Separate onion wedges into petals, and cut chunks of corn kernels from cobs. Add cauliflower florets, onion petals, and corn kernels to bowl with okra and squash. Cover to keep warm.
Chop white parts of scallions to equal 1/2 cup. Coarsely chop green scallion tops, and set aside. Place white scallion pieces in a blender with cilantro, mint, 1/2 cup water, lemon juice, chile, ginger, vinegar, remaining 1 tablespoon oil, and remaining 1/2 teaspoon salt. Process until smooth, about 30 seconds, stopping to scrape down sides as needed.
Add chopped green parts of scallions and torn herbs to bowl with squash mixture; toss gently to combine. Season with salt to taste. Divide rice among plates; top evenly with vegetable mixture, and drizzle with mint chutney.