Set a plate lined with paper towels near the stovetop. Set a heavy 10-inch skillet over medium heat with the pancetta and olive oil. Cook the pancetta, stirring frequently, until light brown and slightly crisp (don't let it fully crisp and harden), about 10 minutes. Remove from the heat and transfer the pancetta with a slotted spoon to drain on the prepared plate (leave the fat in the pan).
Set the skillet back over medium heat and cook the garlic, stirring continually, 30 seconds or until just starting to turn light gold. Transfer the garlic with the slotted spoon to drain with the pancetta.
If less than 1 Tbs. fat remains in the pan, add enough olive oil to compensate. Melt the butter in the pan, add the asparagus, and season with salt and pepper. Sauté, stirring frequently, until the spears are light golden brown and tender (they won't brown evenly) with a slight edge of crispness, 20 to 30 minues.
Transfer the spears to a serving platter, scatter the reserved pancetta and garlic over them, and serve with the lemon wedges.