In a medium sized saucepan of salted water, boil the beans until almost cooked. Drain and put aside.
In a large frypan, heat the oil then add the garlic and cook until fragrant. Add the mushrooms and capsicum then cook until the mushrooms are just soft.
Mix the stock cubes, water and cornflour together.
Add the beans and the stock mix to the frypan, stirring until the sauce has thickened. Cook on low until beans are cooked through.
While the vegetables are cooking, using a separate frypan, heat the pan on high until hot. Spray one side of the steak with cooking spray and sprinkle with salt and pepper. Place in hot pan, sprayed side down, then cook on high for 3 minutes (4-5 minutes if you like it well done).
Spray the top of the steak with spray, sprinkle with salt and flip over in pan. Cook for another 3 minutes. Remove from the pan, place on a tray and cover with foil. Let rest for 5 minutes.
Slice the steak into strips and serve on top of the vegetables.