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 half of 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.