Remove the shells and veins from the shrimp and rinse thoroughly.
Season the shrimp with salt, pepper, and starch.
Heat cooking oil in a pan and sauté the shrimp until golden brown.
Mix chili sauce (ketchup, gochujang, sugar, lemon juice, minced garlic) together.
Add the chili sauce to the cooked shrimp and stir-fry evenly.
Slice onion and bell pepper, add them, and stir-fry together.
Transfer to a plate and garnish with chopped green onion or sesame seeds.