Pat tofu dry with paper towels; cut into ¾-inch (2 cm) cubes. Set aside. Peel and seed squash; cut into ¾-inch (2 cm) cubes to make 3 cups (750 mL). Set aside.
In skillet, heat oil over medium heat; cook onion, garlic and curry paste, stirring occasionally, until onion is softened, about 5 minutes. Add squash, coconut milk, stock, soy sauce, sugar and salt; bring to boil. Reduce heat to low; partially cover and simmer until squash is almost tender, about 12 minutes.
Add red pepper; simmer for 5 minutes. Add tofu; simmer until heated through, about 2 minutes.