Cut the bitter melon in half lengthwise, remove seeds and pith with a spoon, and slice thinly. Slice the garlic.

Boil water in a pot, add salt (not listed in ingredients), and cook spaghetti according to package instructions. Reserve 2 tbsp of pasta water and drain the rest.

Heat sesame oil in a frying pan over low heat, add garlic and chili, and cook until fragrant. Add bitter melon and stir-fry over medium heat until softened. Add tuna and stir briefly.

Add spaghetti, reserved pasta water, black pepper, and soy sauce to the pan. Stir-fry until well combined.