Together with the optimal basic design, buried heterostructure quantum cascade laser (BH-QCL) with semi-insulating regrowth offers unique possibility to achieve an effective thermal dissipation and lateral single mode. We demonstrate here for the first time realization of BH-QCLs with a single step regrowth of highly resistive (>1x10(8) ohm.cm) semi-insulating InP:Fe in less than 45 minutes in a flexible hydride vapour phase epitaxy process for burying ridges etched down to 10-15 mu m deep both with and without mask overhang. The fabricated BH-QCLs emitting at similar to 4.7 mu m and similar to 5.5 mu m were characterized. 2 mm long 5.5 mu m lasers with ridge width 17-22 mu m, regrown with mask overhang, exhibited no leakage current. Large width and high doping in the structure did not permit high current density for CW operation. 5 mm long 4.7 mu m BH-QCLs of ridge widths varying from 6-14 mu m regrown without mask overhang, besides being spatially monomode, TM00, exhibited WPE of similar to 8-9% with an output power of 1.5 - 2.5 W at room temperature and under CW operation. Thus, we demonstrate a simple, flexible, quick, stable and single-step regrowth process with extremely good planarization for realizing buried QCLs leading to monomode, high power and high WPE.