Sesame Beef and Broccoli

1 lb lean beef, cut into bit sized pieces
1 onion, sliced thin
1 lb broccoli florets
1 tbsp sesame seeds

sauce:
1/4 cup peanut butter
2-3 tbsp sesame oil
1 tbsp soy sauce
1 tbsp white wine vinegar
1 tsp chili sauce (sriracha)
1 tsp minced ginger
1 green onion, chopped

Heat a large skillet to medium high heat and spray with cooking spray. Toss in onion and stir fry 2-3 minutes. Add beef and cook 4-5 minutes. Add broccoli and cook 2-3 minutes. In a large bowl or a blender, whisk together all ingredients for sauce, then pour over beef and broccoli. Reduce heat and cook until broccoli is tender and the sauce has thickened; approximately 5 minutes. Serve sprinkled with sesame seeds.