Whisk together all marinade ingredients in a bowl. Add beef and toss to coat. Marinate 1+ hours in the fridge.
Preheat oven to 450°F. Toss onion and snap peas with olive oil on a baking sheet. Season with salt and pepper.
Drain beef from marinade and arrange in a single layer on other side of pan.
Roast 10 minutes until beef is charred and veggies are tender.
Toss with scallions. Serve alongside rice.
Refrigerate leftovers up to 4 days. Can freeze up to 2 months. Reheat until hot before serving.