Prep the ingredients: Wash and dry the fresh produce. Heat a large pot of salted water to boiling on high. Cut off and discard the root ends of the scallions; thinly slice, separating the white bottoms and green tops. Peel and mince the garlic. Remove and discard the kale stems; finely chop the leaves. Quarter and deseed the lemon.
Cook the kale: In a large pan (nonstick, if you have one), heat 2 teaspoons of olive oil on medium until hot. Add the white bottoms of the scallions and half the garlic; season with salt and pepper. Cook, stirring occasionally, 30 seconds to 1 minute, or until fragrant. Add the kale; season with salt and pepper. Cook, stirring frequently, 1 to 2 minutes, or until slightly wilted. Add ¼ cup of water; cook, stirring occasionally, 4 to 6 minutes, or until the kale has wilted and the water has cooked off. Turn off the heat and stir in the juice of 2 lemon wedges. Transfer to a bowl; season with salt and pepper to taste. Wipe out the pan.
Cook the pasta: While the kale cooks, add the pasta to the pot of boiling water. Cook 8 to 10 minutes, or until al dente (still slightly firm to the bite). Reserving ¾ cup of the pasta cooking water, drain thoroughly.
Start the shrimp: Pat the shrimp dry with paper towels; season with salt and pepper. In the same pan, heat 2 teaspoons of olive oil on medium-high until hot. Add the seasoned shrimp in a single, even layer and cook 1 to 2 minutes on the first side, or until lightly browned.
Flip the shrimp. To the pan, add the butter, cooked kale, remaining garlic and as much of the red pepper flakes as you’d like, depending on how spicy you’d like the dish to be; season with salt and pepper. Cook, stirring frequently, 2 to 3 minutes, or until thoroughly combined and the shrimp are cooked through.
Add the cooked pasta and half the reserved pasta cooking water to the pan. Cook, stirring vigorously to coat the pasta, 1 to 2 minutes, or until well combined and heated through. (If the sauce seems dry, gradually add the remaining pasta cooking water to achieve your desired consistency.) Remove from heat and season with salt and pepper to taste. Divide the finished shrimp and pasta between 2 dishes. Garnish with the green tops of the scallions and a drizzle of olive oil. Serve with the remaining lemon wedges on the side, if you’d like. Enjoy!