Heat a large frying pan over medium-high heat. Add the oil when the pan has warmed through. Then add the ground beef, breaking it up as much as possible so the beef can brown. Sprinkle with the salt and pepper. Cook until all the meat has browned, 7 to 10 minutes. Transfer the meat to a bowl.
Dice the onion and mix with the meat. Refrigerate for at least 1 hour (it's easier to create the samosa pocket with cold meat).
When the meat is cool, you're ready to assemble and cook. Create the flour paste by mixing the flour with the water. Add more water or flour until you have a gluey consistency. Slice the cheese into 1/2-inch strips.
Cut the egg roll wrappers down the middle so you create two long rectangles. Drape a damp paper towel over the egg roll wrappers so they don't dry out while you're working. Lay an egg roll wrapper on a clean working surface, the long side facing you. Bring the bottom left corner to the top edge of the wrapper, creating a triangle shape on the left side. Flip the triangle along the right edge of the triangle, so the triangle is sitting on top of flat surface of the wrapper. Keep wrapping in this fashion until you reach the edge. You should have a cone shape with a single flap with two layers of wrapper. Hold the cone in your hand, with the flaps to the back against your fingers and the front seam behind your thumb. Use the flour paste to seal the front seam under your thumb. Stuff the shape with 2 cheese slices and some of the beef and onion mixture. Seal the samosa shut by tucking the interior flap over the filling, then sealing the outer flap to the outside of the samosa with flour paste. Keep assembling until you run out of meat.
Heat 2 inches of oil in a large Dutch oven to 375 degrees F. Deep fry in batches until the skin is golden brown, 2 to 4 minutes. Drain on paper towels.
Mix the ketchup, soy sauce and lemon juice. Serve alongside the samosas. Sprinkle the samosas and ketchup with sesame seeds.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.