Mix together the onion, lemon juice, olive oil, rosemary, minced garlic, salt, pepper and 1 Tbsp honey.
Place chicken in a plastic gallon size bag and pour the marinade on top. Seal tightly and shake to coat. Marinate in the fridge for several hours or overnight.
To prepare: Whisk together the spicy brown mustard, honey and mayonnaise until blended. Set aside.
Heat a couple of drizzles of olive oil in a grill pan over medium-high heat Remove the chicken thighs from the marinade and discard the marinade. Sear the chicken on both sides cooking for 1-2 minutes per side.
After searing, liberally brush the glaze onto the chicken each time you turn the pieces. Cook for an additional 4 minutes total on each side or until the juices run clear. Adjust the cooking time depending on the thickness of the chicken thighs.
Remove to a platter to rest for 5 minutes before serving. Serve over a bed of wild rice or smashed potatoes.