In pot over medium heat, heat oil. Add onions and garlic and cook, stirring regularly, until limp and aromatic. Add tomatoes and cook, mashing with back of spoon, for about 5 minutes or until softened and have released juice. Add fish sauce and continue to cook for about 1 to 2 minutes.
Add water and bring to a boil.
Add squash and cook for about 2 minutes. Add okra, long beans, bitter melon and eggplant. Continue to cook for about 4 to 5 minutes or until vegetables are tender yet crisp. Season with salt and pepper to taste. Add lechon kawali and gently toss until just heated through. Serve hot.
Cook and Prep times are with the assumption that you have lechon kawali cooked and ready.