Place butter in a small microwave safe bowl. Heat in microwave until melted then stir in honey, dijon mustard, olive oil and lemon juice.
Season with salt and pepper to taste. Add half of the honey mustard mixture to a second bowl.
Preheat a grill to 425 degrees. Pound thicker parts of chicken breasts so they are an even thickness and season both sides with salt and pepper. Brush grill grates lightly with oil.
Grill chicken 4 minutes then brush top and with honey mustard glaze (reserving 2nd bowl of glaze for the end).
flip chicken to opposite side, brush second side with honey mustard glaze and continue to grill until chicken is cooked through, about 4 - 5 minutes longer (center should register 165 on an instant read thermometer).
Brush both sides of chicken with remaining glaze from second bowl and let rest on a plate several minutes before serving. Garnish with fresh parsley if desired.