Slice flank steak into pieces that re 1/4 inch/5 mm thick, 2 inches/5 com long and about 1 inch/2.5 cm wide. If you find it difficult to cut thinkly freeze for 15-20 minutes to harden slightly then slice.
Cut peppers into 1 inch squares. Trim ends of long beans and chop into 1 inch pieces. Reserve peppers and beans together.
Heat oil in a wok on heat heat until just about to smoke. Add garlic & curry paste and stir fry about 45 secs. Immediately add coconut milk and lime leaves. Stir-cook about 1/2 minutes until bubbly and thick.
Add beef, bamboo shoots, peppers and long beans all at once. Stir fry 1 minute making sure everything fries in the oil as you're stirring. Add fish sauce and sugar and stir fry 2-3 more minutes until peppers have softened and beef has browned. Add 3/4 of the basil leaves and stir fry from 1 more minute.
Transfer to serving dish and top with red pepper strips and remaining basil leaves. Serve immediately, accompanied with steamed rice.