1. Preheat broiler to high.
2. Place corn and onion on a foil-lined baking sheet. Broil 4 inches from heat for 15 minutes, turning occasionally. Cut bell peppers in half lengthwise; discard seeds and membranes. Place bell pepper halves, skin sides up, on baking sheet with corn and onion. Broil an additional 13 minutes or until all vegetables are charred in spots, turning corn and onion occasionally (do not turn bell peppers). Place bell peppers in a paper bag. Fold to close tightly; let stand 10 minutes. Peel and coarsely chop peppers. Cut kernels from ears of corn. Coarsely chop onion. Place bell peppers, corn, onion, oregano, and 1/8 teaspoon salt in a medium bowl; toss gently.
3. Combine 1/8 teaspoon salt, tomatoes, radishes, 1 1/2 teaspoons oil, and cilantro in a medium bowl; toss to coat.
4. Place 2 tablespoons pumpkinseeds in a mini food processor; process until finely ground. Add remaining 1/4 teaspoon salt, remaining 3 tablespoons oil, jalapeño, and the next 5 ingredients (through garlic); process until smooth.
5. Place 1/2 cup corn mixture in each of 8 shallow bowls, and top each serving with about 2 tablespoons tomato mixture, about 1 tablespoon dressing, about 1 1/2 tablespoons cheese, and about 1 teaspoon pumpkinseeds.