Combine water and bouillon in medium bowl; stir until dissolved. Stir in cilantro, sugar, chili powder, oregano and cumin. Pour into 1-gallon heavy-duty plastic bag. Add flank steak; squeeze out as much air from bag as possible. Marinate in refrigerator, turning steak occasionally, for at least 4 hours or overnight.
Preheat grill or broiler. Remove steak from bag; discard marinade.
Grill or broil using medium heat for 7 to 8 minutes per side or until desired doneness. Let steak rest for 10 minutes before cutting. Cut steak against the grain on the diagonal in thin slices to serve.