Mix cream cheese, onion and garlic together. Spread in the bottom of a shallow dish, onto a cheese board or serving platter. Cover and refrigerate for 30-45 minutes.
Toast the pecans in a 350℉ oven until they become lightly browned and fragrant, about 5-8 minutes. Remove from oven and set aside.
In a small sauce pan over medium to medium-low heat, melt the butter, add the brown sugar, water, Worcestershire sauce, mustard and red pepper flakes. Stir until the sugar dissolves and mixture comes to a low boil (about 5 minutes in all). Remove from heat and stir in pecans.
Remove cheese from the refrigerator, uncover and pour warm pecan mixture over the top. Serve while the topping is warm with sturdy crackers and a cheese spreader.