Melt butter over medium high heat in a frying pan. Place in chicken breast, cook on both sides until nicely browned and cooked through. Remove to a plate and keep warm.
Add green beans to pan and fry in butter over high heat for about 1 minute. Remove to a plate and keep warm.
Add mustard, vinegar and stevia glycerite to pan. Stir to combine. Add cream, stir until combined, heat to boiling and then reduce to a simmer. Let the sauce simmer and thicken for a few minutes.
Add the chicken back to the pan, turning and coating with the mustard sauce. Cook for about 2 minutes.
Divide cauliflower mash and beans between plates. Add a chicken breast to each plate. Serve.