Bring a large pot of salted water to a boil, then add the penne and cook until just al dente, about 10 minutes. Drain and set aside, reserving a small cup of pasta water.
While the pasta cooks, pat the shrimp dry with paper towels to remove excess moisture. Season lightly with salt and pepper.
Heat a large skillet over medium-high heat, then add 2 tablespoons of olive oil. Once shimmering, place the shrimp in a single layer and sear for about 2 minutes per side until they turn opaque and develop a golden, caramelized edge. Use tongs to flip them carefully.
Remove the cooked shrimp from the skillet with a slotted spoon and set aside. Reduce heat to medium.
Add the minced garlic and red pepper flakes to the same skillet. Sauté for about 30 seconds until fragrant, watching closely to prevent burning.
Deglaze the pan with a splash of the reserved pasta water, scraping up any browned bits. Let it simmer for 1 minute, then squeeze in the lemon juice, stirring to combine.
Return the seared shrimp to the skillet, then add the cooked penne pasta. Toss everything together gently to coat the pasta in the flavorful sauce, adding a little reserved pasta water if needed to loosen the sauce.
Turn off the heat and stir in chopped parsley. Taste and adjust seasoning with salt, pepper, or extra lemon juice if desired.
Serve the garlic lemon shrimp penne immediately, garnished with additional parsley if you like, and enjoy the bright, smoky, and tender bites.
