Cook bacon in a large skillet until crisp, then transfer with tongs to paper towels to drain. Reserve 3 tablespoons fat from skillet, discarding remainder. Crumble bacon.
Toast pecans in 2 teaspoons olive oil in skillet over moderate heat, stirring, until 1 shade darker, then transfer to paper towels to drain. Season nuts with salt and pepper and coarsely chop.
Heat reserved fat in a saucepan over moderately low heat until just warm. Remove pan from heat, then whisk in vinegar and remaining 3 tablespoons olive oil until emulsified. Season dressing with salt and pepper.
Toss bacon, spinach, cheese, and half of nuts with enough dressing to coat. Sprinkle salad with remaining nuts.
