Char shucked corn (still on the cob) placing it directly over a gas burner, using tongs to rotate until blackened in spots. (Alternately, cut corn off the cob and add to skillet and saute with zucchini.)
Add onion and zucchini and saute 6 minutes, stirring often. Add jalapeño ( if using) and garlic and continue cooking until zucchini is tender, about 4 more minutes, turing heat down.
In a 10½ inch Skillet, heat oil over medium high heat.