Bring a large pot of salted water to a rolling boil. Add the pasta and cook until just al dente, about 8 minutes. Drain and set aside, reserving a cup of pasta water.
While the pasta cooks, heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add sliced mushrooms and sear, stirring occasionally, until deeply golden and fragrant, about 8 minutes. They should smell smoky and start to crisp around the edges.
Push the mushrooms to the side of the skillet. Add the remaining 1 tablespoon of olive oil, then add minced garlic. Sauté until fragrant, about 30 seconds, making sure not to burn it—the aroma should be bright and pungent.
Place the shrimp in a single layer in the skillet. Sear for about 2 minutes per side until they turn pink, opaque, and have a slight jiggle in the center. They should smell fresh and briny.
Add the cooked pasta to the skillet with the mushrooms and shrimp. Toss gently to combine, allowing the flavors to meld. If the mixture seems dry, add a splash of the reserved pasta water to loosen the sauce and create a glossy coating.
Squeeze fresh lemon juice over the pasta, then season with salt, pepper, and chili flakes if using. Toss again, tasting and adjusting seasoning as needed. The dish should smell bright with citrus and smoky with mushrooms.
Cook for another minute, allowing the sauce to coat the pasta evenly. The mixture should shimmer with a glossy finish, with the shrimp juicy and the mushrooms deeply golden.
Transfer to serving plates, sprinkle with chopped parsley, and garnish with lemon wedges. Serve immediately while hot, enjoying the tender shrimp and smoky mushrooms in every bite.
