Vegan Thai-Spiced Candy Potato Stew

1 tablespoon olive oil
1 medium onion, quartered and thinly sliced
4 to six garlic cloves, minced
3 medium candy potatoes (about 1-1⁄2 kilos), peeled and diced
3 cups water
1 medium inexperienced or purple bell pepper, minimize into slender strips
1-1⁄2 cups frozen inexperienced beans
1⁄2 teaspoon purple or inexperienced curry paste, or to style
1 tablespoon sugar
2 teaspoons minced contemporary ginger
2 stalks lemongrass (elective)
1 (13.5-ounce) can mild coconut milk
2 tablespoons peanut butter
Salt to style
1 (8-ounce bundle) Thai peanut-flavored baked tofu, diced (elective)
Cilantro leaves for garnish