Heat butter in a large skillet over medium heat, stirring occasionally, until lightly browned, 1 to 2 minutes. Cook and stir onion in hot butter until translucent, about 5 minutes.

Cut kernels from ears of corn. Add kernels and zucchini to onion in the skillet; cook and stir until zucchini is tender, about 8 minutes. Season with sea salt and black pepper.