Marinade: In a medium bowl, mix together the onion, lemon juice, olive oil, rosemary, minced garlic, salt, pepper and 1 Tbsp honey.
Place chicken thighs into a plastic gallon size bag and pour the marinade on top. Seal tightly and shake to coat. Marinate in the fridge for several hours(at least 4 hours) or overnight.
Honey Mustard Glaze: In a small bowl whisk together the honey, spicy brown mustard 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. (If grilling, heat the grill to medium-high heat, then lower the heat to medium after adding the chicken.)
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.