Heat a large non-stick frying pan over a moderate heat. Cook sausages for 10 minutes or until cooked, turning occasionally. Remove from pan and add 2 teaspoons oil. Add eggs and swirl to cover base of pan. When underside is brown, turn omelette over and cook until set. Remove from pan. Coarsely chop sausages and omelette. Cover and set aside.
Add remaining oil to pan. Cook onions for 5 minutes, stirring occasionally. Cut leaves from gai lan and slice into 4cm lengths. Cut stems into 4cm lengths, slicing the thick stems in half lengthways. Add garlic and gai lan stems to pan and increase heat; stir for 2 minutes. Add curry paste and stir until fragrant, then add gai lan leaves and cook until wilted.
Add rice and stir until well combined, then add cherry tomatoes, sausages and omelette and stir until heated through
Stir in fish sauce and sugar, then Thai basil leaves. Serve with sliced cucumber and lime wedges.
Store cooked rice covered in the refrigerator for at least 6 hours or overnight. This allows the rice grains to dry and separate.