In a large pot of boiling salted water, cook the linguine according to package instructions until al dente. Drain and set aside, reserving about 1/2 cup of the pasta cooking water.
Season the flank steak slices with salt, pepper, smoked paprika, and cayenne pepper. Make sure to coat each piece evenly.
In a large skillet over medium-high heat, add about 1 tablespoon of the melted butter. Once hot, add the steak in a single layer. Sear for 2-3 minutes on each side until browned and cooked to your desired doneness. Remove the steak from the skillet and allow it to rest.
In the same skillet, lower the heat to medium. Add the remaining melted butter, minced garlic, and lemon zest. Cook for about 30 seconds until fragrant, being careful not to burn the garlic.
Add the drained linguine into the skillet with the garlic-butter mixture. Toss to coat the pasta evenly, adding a splash of the reserved pasta water if needed for moisture. Add the lemon juice and half of the chopped parsley, mixing well.
Slice the rested steak into bite-sized pieces. Plate the linguine and top it with the sliced steak. Garnish with the remaining parsley, a sprinkle of grated Parmesan cheese, and cherry tomatoes if using.
Notes
Adjust the cayenne pepper for spice tolerance. Optional cherry tomatoes can add freshness.