Preheat oven to 375ºF. Line a baking sheet with aluminum foil. Lay a few layers of paper towels on top of a cooling rack and place near the oven.
Glaze and bake the bacon until crispy: Arrange the bacon in a single layer on the baking sheet. Brush with 1 1/2 tablespoons of barbecue sauce.
Transfer to the oven and bake until crisp and caramelized, 15 to 20 minutes (begin checking around 15 minutes; the bacon could take up to 20 minutes to fully crisp depending on the brand).
Remove the bacon from oven and drain for a few minutes on paper towels, then transfer to a plate to finish cooling. The pieces will stick to the paper towels if left for too long.
While bacon cooks, prepare the filling: Combine cream cheese, cheddar cheese, chives, garlic and barbecue sauce in a small mixing bowl.
Prepare the jalapeño peppers: Wear gloves for this step if you are sensitive to pepper heat. Cut the jalapeños in half lengthwise. Use a spoon to scoop out the seeds. You can leave the stems on (they make nice handles for eating!) or trim them off. Arrange all the jalapeños cut-side up on a platter.
Stuff the peppers: Chop or crumble bacon into small bits, then fold into the cream cheese mixture. Using a spoon, fill each of the jalapeño halves with a big dollop of the cream cheese mixture, mounding slightly.
At this point, the poppers can be covered and refrigerated until ready to grill.
Prepare your grill: For gas grills, heat the grill with the burners set to high and preheat for 10 minutes. When ready to grill, reduce the burners to medium.
For charcoal grills, fill a grill chimney with charcoal and light it. When the coals are hot (they should be covered with a layer of fine gray ash) empty the coals into the grill and push them to one side of the grill to make higher heat and lower heat cooking zones. Set the grate in place and cover the grill. Preheat the grate for 5 minutes.
Grill the poppers: Brush grill grates with oil to prevent sticking. If you're using a charcoal grill, cook over the low-heat cooking zone.
Using tongs, place the poppers on the grill so they lay across the grates and don't fall through. If any of the poppers is leaning to the side, prop it up against a neighbor so the cheese filling doesn't start to melt out as the poppers cook.
Grill until the poppers are seared on the bottoms and the cheese filling is hot and bubbling around the edges, about 10 minutes. Be careful of overcooking or the peppers will become too soft.
Serve the poppers right away: Using tongs and a spatula in tandem to scoop up the poppers, remove from the grill and transfer to a platter. Serve immediately alongside sour cream, if desired. Discard the stems as you eat.