For the steak: Place the steak on a baking sheet or in a dish and rub with garlic and olive oil. Sprinkle all over with salt and pepper. Let sit for 10 minutes.
Preheat a grill or grill pan over high heat. Brush the steak with some teriyaki sauce. Grill the steak until medium rare, about 6 minutes on each side. Remove the steak from the grill and let sit.
For the vegetables: Heat the olive oil and butter in a large deep skillet over medium-high heat. Add the peppers, zucchinis and onions, and saute for 5 minutes, stirring. Season with salt and pepper.
Slice the steak thinly against the grain. Serve with the vegetables.