In a large skillet, heat 1 tablespoon oil over medium-high. Add garlic and zucchini, season with salt and pepper, and saute until zucchini is tender and browned in spots, about 6 minutes. Transfer to a bowl.
Add remaining tablespoon oil to skillet. Season steak with salt and pepper and cook until browned, 4 to 5 minutes per side. Transfer to a plate and loosely tent with foil.
Discard fat from skillet, then add vinegar, 1/2 teaspoon salt, and 2 teaspoons pepper. Cook, stirring, until reduced by half, about 2 minutes. Slice steak; add any accumulated juices from steak to skillet and stir to combine. Drizzle steak with sauce and serve alongside zucchini.