Cob-smoked bacon imparts a hearty flavor without overpowering the scallops. If you can't find the cob-smoked variety, substitute any good wood-smoked bacon. Petite New England bay scallops are the perfect size for this dish; they're sweeter, too. But sea scallops are always delicious.
In a large sauté pan over medium heat, cook bacon until done but not crisp, about 10 minutes. Remove bacon, and drain on a paper towel. Pour rendered bacon fat into a cup and set aside.
Chop bacon when cool. Meanwhile, in a large pot, cook pasta according to package instructions. When done, drain and put back into the empty pot.
Add olive oil to the sauté pan and raise heat to medium high. Sprinkle scallops with salt and pepper; then add to the pan in batches to avoid overcrowding. Sear on one side, then the other, until lightly browned, about 3 minutes. Set aside. Repeat with remaining scallops.
Add lemon juice to pan, stirring to release the browned bits on the bottom. Add 2 tablespoons reserved bacon fat. Add garlic and shallots and sauté over medium heat until tender, about 5 minutes. Add spinach and sauté until just wilted.
Remove spinach and toss with pasta. Add bacon and scallops. Sprinkle with more bacon fat to taste. Add red-pepper flakes if you like.