Heat extra virgin olive oil in a large non-stick skillet over medium heat. Add the bacon and cook until just crisp, about 6 minutes. Reduce heat to medium-low. Stir in garlic, leek, lemon zest and thyme; cook until softened, about 5 minutes. Stir in cream cheese until melted. Stir in chicken stock until smooth, about 2 minutes.
Meanwhile, cook spaghettini in a large pot of boiling salted water until al dente, about 3 minutes. Reserve ½ cup pasta water and drain pasta.
Increase skillet heat to high. Stir in pasta water and pasta; season with salt and pepper. To serve, stir in freshly chopped chives.