Pat tofu dry with paper towel; cut into 3/4-inch (2 cm) cubes. Set aside.
In saucepan, heat oil over medium-high heat; sauté onion, garlic, mushrooms, lemon juice and lime rind and hot pepper flakes until liquid is evaporated- 5 minutes. Add stock, tofu and sugar; bring to boil. Reduce heat, cover and simmer for 8 minutes.
Add asparagus, green onions and coriander leaves; simmer, covered, until asparagus is tender-crisp- 2 minutes. Add lime juice and let it simmer for another minute.