Ginisang Ampalaya (Sauteed Bittermelon)

3 medium sized bittermelon (seeded and sliced into half then into 1/4")
1 cup shelled shrimps (cut to pieces)
1 cup sliced yellow onion
1 cup chopped roma tomatoes
1 tablespoon minced garlic
4 tablespoons fish sauce
1 pinch salt
dash of freshly grated black pepper
1 egg