Heat a griddle or large, heavy-based frying pan over a high heat.
Thread 5 cubes of beef each onto a skewer. Brush the beef with a little olive oil and season with freshly ground pepper only.
Squeeze the roasted garlic into a food processor with the grain mustard and the cream, blend for 15 seconds and reserve.
Cook the beef skewers on the preheated griddle. Cook for 1 and a half minutes on each side for rare, longer if you prefer your beef well done.
Heat the remaining olive oil and the butter in a wok. Toss in the green beans and the pepper strips. Fry, stirring often, for 2 minutes, while the beef is griddling. Add a squeeze of lemon juice and season the beans with salt and freshly ground pepper.
Let the beef rest while placing the bean and pepper mixture on a plate. Top with the beef skewers and drizzle over the reserved mustard garlic cream.