Begin by heating oil in a large pan over medium heat. Add chopped onions and cook until they turn clear and soft. Stir in minced garlic and cook until you can smell its aroma.
Add your ground beef to the pan. Break it apart into small pieces with your spoon while it cooks. Keep cooking until the meat turns brown and is no longer pink.
Pour in the fish sauce and let it cook with the meat for 2 minutes. Now, if you're making soup, add your chopped fresh tomatoes and cook until they become soft. For stew, use tomato sauce and crushed tomatoes instead.
Add your liquid - use 2 cups of broth or water for soup, or just ½ cup for stew. Let it come to a boil, then lower the heat to simmer. Add your cubed potatoes now. If you're making stew, also add your carrots and raisins.
Cover your pan and cook everything for about 15 minutes, or until you can easily pierce the potatoes with a fork. For the stew version, this is when you add your green peas and olives - they only need about 3 minutes to cook.
Taste your dish and add salt and pepper as needed. If you're making stew, keep cooking until the sauce thickens up - about 5 more minutes. For soup, you're ready to serve once the potatoes are tender.
Let your picadillo rest for 5 minutes before serving. This helps all the flavors come together. Serve hot over freshly cooked rice. If you like, you can add some chopped green onions on top or serve with calamansi on the side.
Remember: The meat and potatoes should be tender, and the stew version should have a thick, rich sauce while the soup version should be brothy. Enjoy your homemade picadillo.