Heat broiler. In a medium ovenproof (preferably cast-iron) skillet, heat oil over medium heat and cook onion and jalapeno, stirring, until tender, about 5 minutes. Add zucchini and corn and cook until tender, about 7 minutes more. Season with salt.
In a bowl, whisk eggs with 1/2 teaspoon salt and pour into skillet with vegetables. Cook until sides are just beginning to set, 2 to 3 minutes.
Transfer skillet to oven and broil until just set in the middle and lightly golden and puffed on top, 2 to 3 minutes.
The Mild Side
Prefer less heat? Remove the seeds and membrane from the jalapeno.