Mix the Dijon, honey, vinegar, salt and pepper, and the 1 tablespoon minced thyme.
Place chicken in a large bowl or zip-top bag and add about two-thirds of the Dijon mixture. Refrigerate chicken and extra sauce until ready to grill, although it is fine to grill immediately.
Over medium heat, grill chicken thighs for about 5 minutes per side, or until just cooked through, basting occasionally with remaining sauce. (Grilling time will be a bit longer if the thighs have not been pounded.)
Allow to sit for 5-10 minutes before serving and garnish with a little minced thyme and a lemon slice or wedge.