NOTE: Aji panca, aji amarillo and queso fresco can be found at Hispanic markets. You may be able to find the cheese at a well-stocked grocery store as well.
Remove heads and shells from shrimp, and refrigerate the shrimp. Put shells and heads in a medium saucepan, add water to cover, and bring to a boil over medium-high heat. Reduce the heat and simmer for 15 minutes.
While shells are simmering, heat the olive oil in a large flameproof casserole over medium heat. Add onion and garlic, and cook for 2 minutes, stirring. Stir in the aji panca (or tomato paste) and aji amarillo pastes. Reduce heat to medium-low and continue cooking, stirring often, for 10 minutes, or until onion is softened.
Puree shrimp shells and cooking liquid. Strain mixture through a fine-mesh strainer into a bowl and reserve the liquid (solids can be discarded). Measure out the liquid and add enough water to make 4 cups.
Add shrimp broth to onion mixture and bring to a boil. Stir in peas, rice and corn chunks. Reduce the heat and simmer for 10 minutes.
Add potatoes and salt. Continue cooking until potatoes and rice are just tender (approx 10 minutes more). Add shrimp and queso fresco. Simmer, stirring occasionally, until shrimp is just cooked through, about 4 minutes (shrimp should be pink).
Stir in the evaporated milk and oregano. Continue cooking and stirring. When the soup begins boiling again, Crack the eggs into the soup, spacing them so they remain separate in the soup. If you prefer, you can beat the eggs together in a bowl before adding them to the soup instead).