Mix the oyster sauce, fish sauce, Sriracha, sugar and 1/4 teaspoon salt in a small bowl; set aside. Heat 1 tablespoon vegetable oil in a large nonstick skillet over medium-high heat. Blot the tofu cubes dry and add to the skillet in a single layer. Season with salt and pepper and cook, turning occasionally, until browned and crisp, 5 to 6 minutes; remove to a plate.
Add the remaining 2 tablespoons vegetable oil to the same skillet over medium-high heat. Add the green beans, garlic and a pinch of salt. Cook, stirring, until the garlic is lightly browned, about 1 minute. Add the rice and 1/2 teaspoon salt; cook, stirring, until heated through, 2 to 3 minutes.
Add the oyster-sauce mixture, browned tofu and bean sprouts to the skillet. Stir until heated through, about 1 minute; season with salt and pepper.
Divide the fried rice among bowls and top with basil, scallions and cashews. Serve with lime wedges and more Sriracha.