In a large pot, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic, smoked paprika, and red pepper flakes. Cook for an additional 1-2 minutes until fragrant.
Pour in the chicken broth, diced tomatoes, and water. Bring the mixture to a boil, then reduce the heat and simmer for 10 minutes.
Add the shrimp to the pot and cook until they turn pink and opaque, about 3-5 minutes.
Stir in the chopped cilantro, lemon juice, and season with salt and pepper to taste.
While the soup is simmering, toast the slices of bread until golden brown.
Serve the soup hot, garnished with grated Parmesan cheese if desired, alongside the toasted bread.