Pat steak dry, slice against the grain in 1” thick strips and sprinkle with 1/2 tsp salt and 1/2” tsp black pepper.
Heat 2 tbsp olive oil and 2 tbsp butter in a skillet over medium, add steak and saute for approximately 5 minutes for medium.
Remove steak from the skillet, add remaining butter, onion, garlic and saute for a minute.
Add bell peppers and saute for two minutes, return the steak to the pan and saute together for 30 seconds.