In a bowl, mix onion powder, garlic powder, paprika, chili powder, cayenne pepper, salt, and black pepper. Coat the chicken thighs with this spice rub evenly.

In a small saucepan, combine the diced peach and sugar. Bring to a boil, then lower the heat and simmer for 5 minutes while stirring occasionally.

Add the BBQ sauce and lemon juice to the saucepan. Continue to simmer for another 5 minutes, then blend the mixture until smooth using an immersion blender or a regular blender. Set aside.

Preheat the grill to medium-high heat. Grill the seasoned chicken for 3 to 5 minutes on each side to develop a char.

Brush the peach BBQ sauce over the chicken, grilling for 1 minute on each side. Repeat this process by adding another layer of sauce and grilling for an additional minute on each side. Ensure the chicken reaches an internal temperature of 165°F.

Remove the chicken from the grill and let it rest. Meanwhile, brush the quartered peaches with the BBQ sauce and grill them for 1 to 2 minutes per side.

Serve the chicken with the grilled peaches and additional sauce on the side.