Boil a pot of salted water and cook the linguine pasta according to the package instructions until al dente. Drain the pasta, reserving one cup of the pasta water for later use.
In a large skillet, melt a tablespoon of butter over medium heat. Add the finely chopped garlic and sauté for a minute until fragrant, being careful not to burn it. Add the shrimp and cook for a few minutes until they turn pink and opaque. Remove the shrimp from the skillet and set them aside
Saute diced onions in the same pan until translucent. Add tomatoes paste, sun dried tomatoes and sliced mushrooms Sauté them for a few minutes until they are softened.
Pour in the heavy cream or half and half to the skillet and stir to combine with the tomato paste mixture. Add some of the reserved pasta water to thin out the sauce.
Add salt, pepper, crushed red pepper and Italian seasoning and stir.
Add in the spinach leaves and allow to wilt in the sauce, and add in the Parmesan cheese.
Add cooked shrimp and cooked linguine pasta to the skillet with the sauce and toss it well, ensuring the pasta is evenly coated with the garlic butter Tuscan sauce.