Bring 3 cups of water to a boil in a medium saucepan over high heat, covered. Uncover and slowly whisk in the grits, salt & pepper. Reduce heat to medium-low and cook, stirring occasionally, until thickened, approximately 5 minutes. Stir in the Parmesan cheese and 1 tbsp butter. Remove from heat and season with salt and black pepper. Cover to keep warm. Meanwhile, season the shrimp with salt, black pepper, and lemon zest. Melt the remaining 2 tbsp butter in a large skillet over medium-high heat. Add the shrimp, garlic and red pepper flakes, and cook, tossing, until the shrimp are pink, about3-4 minutes. Remove from the heat and add 2 tbsp water, lemon juice, and parsley. Stir to coat the shrimp with the sauce and season with salt and black pepper. Divide the grits among shallow bowls and top with the shrimp and sauce. Serve with lemon wedges.