The Pb-islands growth on a clean vicinal Si(557) surface at room temperature has been studied using Scanning Tunneling Microscopy. We observed anisotropic tilted wedge-shaped Pb-islands to grow following the Stransky-Krastanov scenario. The elongation of the islands along the step edges of Si is associated with the anisotropic potential of the vicinal template. It was demonstrated that the growth of tilted Pb bulk islands is accompanied by their separation into layers which is clearly observed in the STM images as a slab-like stacking morphology, and also appearing from the statistical analysis. The single layer preferable thickness in the slab-like stacking like structure was found to be 2nm, which corresponds to 7 Pb monolayers. The results discussed in terms of electronic growth model. Using DFT simulations we argue that such growth mode is realized due to the minimization of the electron energy owing to the quantum confinement inside the created quantum wells. The growth mechanism can be explained in the framework of the electronic growth model including the interfacial strain and twin boundary formation. DFT simulation support that preferable position for Pb atom during growth of the 8th layer is hcp i.e. twinning boundary creation.