Halve tofu lengthwise. Cut each half crosswise into 4 pieces.
Heat 1 tablespoon oil in a large nonstick skillet over medium-high. Add tofu to pan; cook, without stirring, until lightly browned, 4 to 5 minutes. Turn; cook 2 minutes.
Carefully add soy sauce to pan; cook 2 minutes. Turn tofu; cook 1 minute.
Remove from pan; let cool. Cut each piece diagonally into triangles.
Combine ¼ cup water and coconut milk in a bowl.
Heat remaining 1½ tablespoons oil in a large skillet or wok over high until oil is hot but not smoking. Add shallots, chiles, and lemongrass; cook 1 minute or until fragrant, stirring constantly.
Add salt, green beans, and bell pepper; cook 2 minutes or until vegetables have softened slightly.
Add curry and sugar; cook 1 minute, stirring constantly.
Add tofu, milk mixture, and fish sauce; cook 2 minutes or until thoroughly heated.
Arrange tofu mixture on a platter.
Sprinkle with cilantro to serve