Peel shrimp and place skin, heads, and tails into a large saucepan. Fill pan with water and bring to a boil. Reduce heat to low and let simmer, about 45 minutes.

Combine tomatoes and 1/2 the parsley in a blender; puree until smooth.

Heat olive oil in a separate pan over medium heat. Add onion, bell pepper, and chile pepper; cook and stir until softened, about 5 minutes. Add garlic; cook until fragrant but not browned, 1 to 2 minutes.

Pour pureed tomato mixture into the pan with the peppers. Add water, tomato paste, oregano, salt, and black pepper. Stir well; add paprika. Let sauce simmer on low to medium heat until juices have reduced.

Strain shrimp shells from the water. Bring water back to a boil and add spaghetti. Cook spaghetti, stirring occasionally, until tender yet firm to the bite, about 12 minutes. Reserve 1 cup of the cooking water and drain the rest.

In the meantime, add shrimp to the tomato sauce. Add the reserved water, stir well, and cook until shrimp is pink, about 3 minutes. Plate spaghetti and spoon the sauce on top; garnish with the remaining parsley.