Cachichín (Oecopetalum mexicanum) is a tree that grows naturally in the ecotone between low deciduous forest and high semi-evergreen forest in the Sierra de Misantla, Veracruz, Mexico. The fruit produces an oval nut-like seed, with a thin outer layer and a smooth texture. The region’s inhabitants enjoy this food in its raw, boiled, and toasted forms, considering it a traditional and nutritious snack. However, its nutraceutical value remains largely unknown, while the effects of the processing methods it undergoes before consumption has not yet been explored. The aim of this study was to asses changes in the color, water activity, and fatty acid profile of the raw cachichín seed (T1) and compare it with three thermal treatments: boiling (T2), commercial toasting (T3), both performed empirically by local vendors in the region, and controlled toasting under laboratory conditions (25 min at 134 °C) (T4). Water activity (aw) and color (CIELab*) were quantified using a Hunter-Lab colorimeter, also obtaining color difference (∆E), chromaticity (C*), and hue angle (H°). The fatty acid profile was analyzed using gas chromatography with a FID detector. The results demonstrated that thermal treatments, compared to raw seeds (T1), significantly affected the water activity and color parameters of the cachichín seed. Lipid analysis revealed the presence of oleic acid (ω-9), linoleic acid (ω-6), and linolenic acid (ω-3), with significant differences observed mainly between T1 and T3; treatments T2 and T4 showed intermediate values. Notably, commercial tasting (T4) resulted in significantly different water activity and color parameters compared to the boiled treatment (T2). Additionally, the raw seed retained a higher fatty acid content, while commercial toasting led to a greater loss of these compounds. These findings have important implications for the selection of the cooking method, depending on the desired characteristics of the final product, such as the texture, flavor, and preservation of bioactive compounds.