installing steel lentil to CMU(cinder block) wall?

if you are using cement blocks, (unless they are 4 in. blocks) you will need to place 2 angles back to back and notch your block to go over the center (bond beam blocks), the angles just sit on the side walls and the blocks are usually laid with a dry bed joint...and you of all people should know chica that there arent cinder blocks any more...they are cement blocks...if the angles are being heated to any great degreee you might want to put a thin layer of fiberglass insulation on top of the angle to compensate for expansion...

Do not do this if you want a good long lasting job. Moisture from the shower and vapor from the block work both ways. A plastic liner first attached to the wall then cement backerboard lagged to the wall will give a better result. Not perfect but better. If you just attach the tiles the vapor that comes through the walls will affect either the grout or the block itself causing it to efforvescence making the bond less strong. Painted areas should also be avoided to attach tiles to. Once again the vapor and water work both ways. Once you get the tiles up really pay attention to the condition of the grout and any cracks that develop along the sides to repair them as soon as possible. Also take into account the moisture that you are getting in the basement naturally. Is it a 'dry' basement or do you have water problems. It may be that it would be less hassle to just paint the wall in the shower and be able to maintain the paint than going to all the effort of tiling methods just to have a mold machine.

Unless you are using beans I think you mean "lintel". :) An angle iron laid in the grout joint would probably be sufficient for what you are doing but without knowing the load I would hesitate to offer advice. Search lintel instead of lentil and you should find your answer.