Preheat oven to 425°. Arrange bacon strips lengthwise in a foil-lined 15x10x1-in. pan, overlapping slightly.
Cut tenderloin lengthwise through the center to within 1/2 in. of bottom. Open tenderloin flat; pound with a meat mallet to 1/2-in. thickness. Place tenderloin on center of bacon, perpendicular to strips.
Sprinkle pepper over pork. Spread with pesto; layer with cheese and spinach. Close tenderloin; wrap with bacon, overlapping ends. Tie with kitchen string at 3-in. intervals. Secure ends with toothpicks.
In a 12-in. skillet, brown roast on all sides, about 8 minutes. Return to baking pan; roast in oven until a thermometer inserted in pork reads 145°, 17-20 minutes. Remove string and toothpicks; let stand 5 minutes before slicing.
