Combine shrimp with lemon juice and a couple of generous splashes of Tabasco sauce; let sit while you begin the grits and gravy.
Make the grits: in a large heavy saucepan, bring 6 cups water and 1 teaspoon salt to a boil.
Whisk in the grits a few handfuls at a time (they will bubble up initially).
When you have added all the grits, decrease heat to a very low simmer and cook over low heat for 35-40 minutes, stirring occasionally at first and more frequently toward the end.
While the grits simmer, start the gravy: fry bacon in a skillet over medium heat until brown but still limp; stir in the onion, green pepper, and garlic; continue cooking until onion and pepper are limp, about 5 minutes.
Add in the scallions; sprinkle flour over the mixture; continue sautéing for 5 minutes longer.
Stir in the stock and remaining salt; cook for 5 minutes longer; remove from the heat while you finish the grits.
When the grits are thick and creamy, stir in as much of the butter as you wish, followed by the cheese.
Add a splash of Tabasco sauce and more salt if desired.
Cover the grits while you finish the gravy.
Return the gravy to the heat and stir in the shrimp; cook until the shrimp are opaque throughout, about 5 minutes.
Serve immediately mounding the grits in large shallow bowls or on plates and covering them with shrimp and gravy.