Heat the olive oil in a large skillet over medium heat. Add the onion and cook, stirring often, for 2 minutes. Add the corn and lima beans and cook, stirring often, for 3-4 minutes. Add the zucchini, sea salt, and freshly cracked pepper, to taste. Cook for an additional 2 minutes then pour into a serving dish.
Let the succotash cool for a few minutes before adding the tomatoes, cilantro, and avocado, mixing gently.
Taste and re-season if needed. Top with cotija cheese crumbles. Serve immediately. Enjoy.