Have all ingredients ready for stir-frying: Cut asparagus into 2-inch (5 cm) diagonal pieces; cut onion and tomatoes into wedges; cut cucumber in half lengthwise, then into 1/4-inch (6 mm) chunks; peel shrimp.
In saucepan, combine sugar, cornstarch, water, lemon juice and vinegar; bring to boil, stirring. Cook 1 or 2 minutes until thickened. Season to taste with salt, and add a few drops yellow food coloring if desired. Keep sauce warm while stir-frying.
In large skillet or wok, heat 2 tablespoon (25 mL) oil. Add asparagus and stir-fry for 1 minute. Add water and sprinkle lightly with salt; cover and steam until asparagus is nearly tender, about 2 minutes. Remove asparagus and set aside. Drain skillet.
Add remaining oil to skillet. Brown onion and ginger lightly; remove ginger. Add shrimp and stir-fry for 2 minutes. Add cucumber, tomatoes and asparagus; cover and steam for 2 or 3 minutes just until tender-crisp. Taste and adjust seasoning.
Stir in lemon sauce and lemon slices; bring to boil, stirring gently. Serve immediately.
3/4 cup Granulated sugar
1 tablespoon Cornstarch
1/2 cup Water
1/4 cup Lemon juice
2 tablespoon Vinegar
Yellow food colouring (optional)