In a large pot of boiling salted water, cook pasta until al dente. Reserve 1/2 cup pasta water; drain pasta, and return to pot.
While pasta is cooking, fry bacon in a large skillet over medium until browned, 6 to 8 minutes. Using a slotted spoon, transfer to a paper-towel-lined plate.
Add shrimp, scallions, and garlic to skillet. Cook, stirring frequently, until shrimp are almost opaque, about 1 minute. Add cup pasta water, and bring just to a boil.
Add shrimp mixture and lemon juice to pasta. Season with salt and pepper, and toss to combine. Thin sauce with pasta water as needed. Serve sprinkled with bacon.