Mango kernel flour was produced through solid-state fermentation (SSF) by Aspergillus oryzae and Aspergillus awamori for 48 and 96 h at 30 °C, followed by a washing step to remove simple carbohydrates (water-soluble fraction, MKWF). The results show that SSF by A. oryzae reduces phytic acid content by more than 60% after only 48 h and increases the protein content in the flour by more than 55% after 96 h. SSF by A. awamori and A. oryzae increases fat content by more than 49 and 25%, respectively. The free sugars recovered in the MKWF are useable by L. plantarum, which achieved at least one log10 CFU/mL of growth. The MKWF also contains a significant amount of malto-oligosaccharides which might be of interest for its prebiotic use. Mango seed kernel can be upcycled through SSF by Aspergillus spp into a functional flour and an MKWF suitable for Lactobacilli biomass production.