Heat half the oil in a large skillet over medium-high heat. Add half the zucchini and cook, stirring only occasionally, until golden brown, 10 to 12 minutes. Transfer the cooked zucchini to a plate. Repeat with the remaining oil and zucchini.
Return the first batch to the skillet. Stir in the garlic, marjoram, 1/2 teaspoon salt, and 1/4 teaspoon pepper and cook, stirring, for 2 minutes.