Prepare the spaghetti omelette mixture: In a bowl, combine diced tomato, diced onion, diced green bell pepper (or jalapeno), sardine, white pepper powder, bouillon powder, eggs, and cooked spaghetti. Whisk together until well combined.
Heat the skillet: Place a skillet on medium heat and add olive oil. Allow the oil to heat up.
Cook the spaghetti omelette: Pour the spaghetti egg mixture into the skillet, spreading it out evenly to form a single layer touching the pan. Reduce heat to low and cover the pan. Cook slowly for about 5 minutes to avoid burning and ensure the egg sets without runniness.
Flip and finish cooking: Once one side is set, carefully flip the omelette and cook the other side for another 3 to 4 minutes until fully cooked and slightly crispy around the edges.
Prepare the sandwich: Slice open the French baguette. Spread mayonnaise on one side and pepper sauce on the other side of the bread. Fill the bread generously with the cooked spaghetti omelette.
Serve: Cut the sandwich in half and serve immediately, enjoying the crispy edges and fluffy middle of the spaghetti omelette inside the soft bread.