Drain tofu from packing liquid. Pat with paper towels to absorb excess liquid. Cut into 1/2-inch cubes.
In a wide pan over medium heat, heat about 2 tablespoons oil until very hot. Add tofu and cook, turning as needed, until lightly browned. Remove from pan and drain on paper towels.
Wipe down the pan as needed. Heat another 1 tablespoon of oil.
Add onions and garlic and cook until softened.
Add fish sauce and cook for about 1 minute.
Add singkamas, carrots, and sweet potatoes.
Add water and bring to a boil. Lower heat, cover, and continue to cook until vegetables are tender yet crisp.
Add tofu, garbanzo beans, and green beans, stirring to combine.
Season with salt and pepper to taste.
Continue to cook for another 2 to 3 minutes or until garbanzo beans and tofu are heated through and green beans are tender yet crisp.
Remove from the pan and drain excess liquid. You can use this liquid to make the sauce and just add water to total 2 1/2 cups.