Cut the meat, bell peppers and onion into squares.
In a large bowl, whisk the jar of Maille(R) Dijon Originale mustard, olive oil, thyme, salt and pepper. Add the meat to the mixture and coat evenly. Refrigerate for 30 minutes. Alternate the meat with the bell pepper and onion squares on skewers. Grill, turning frequently and brushing with the remaining mixture.