In a large pot cook the pasta in salted boiling water according to package directions. Drain and set aside.
Using the same pan, heat olive oil and 2 Tbsp of butter. Add the garlic and red pepper flakes and cook until fragrant 1-2 minutes.
Add the shrimp and salt. Cook until the shrimp start to turn pink. Add spinach and cook until wilted.
Add the pasta back to the pot with the remaining butter and parmesan. Stir until mixed and butter is melted.
Add the lemon juice, stir again and serve hot.