Prepare a grill for medium heat cooking.

Bring a large pot of water to boil and add salt.

Blanch zucchini and bell peppers separately for about 1 minute each.

Remove zucchini and bell peppers with a slotted spoon as done and drain well in a colander.

Transfer to paper towels.

In a large bowl, gently toss zucchini, bell peppers, tomatoes, and onions with oil.

Place oiled vegetables on hot grill, 7 inches above gray flaming coals, if using charcoal.

Place corn on the cob on grill at the edge of hottest part of grill.

Turn vegetables to ensure grill marks on all sides and cook until just until crisp-tender for zucchini, bell peppers and corn and until tomatoes become slightly soft and heated through, about 6 to 8 minutes.

Meanwhile, preheat the oven to 400°F.

Wrap tortillas in foil and heat for 3 to 5 minutes, just until warm.

Remove grilled vegetables and slice zucchini, bell peppers and tomatoes into bite-size pieces.

Remove corn kernels from cobs and transfer all grilled vegetables to a large platter.

Serve fajitas with cilantro, salsa, cheese, and sour cream on the side.