Plant-based egg analogs often fail to develop characteristic egg aroma, which limits their sensory acceptance. While the pronounced differences in key aroma compounds between chicken egg and vegan egg products have been identified, the precursor-driven mechanisms underlying these differences remain unclear. The HPLC-MS technique was used to measure the free amino acids of scrambled chicken eggs and a commercial plant-based egg product before and after cooking. This first comparative analysis revealed pronounced deficits in key free amino acids involved in egg aroma chemistry, particularly methionine, cysteine, glutamic acid, and aspartic acid, in the plant-based matrix. To address this gap, 23 plant-derived raw materials were analyzed for their free amino acid composition, generating a targeted comparative dataset that links naturally occurring free amino acids in plant ingredients to egg-relevant aroma precursors. Oyster mushroom, yeast extract, cucumber, and celery root were identified as the most effective contributors to the missing precursor pool. These findings were translated into three prototype formulations designed to restore precursor availability. Consumer test results (n = 58) reported that the prototype enriched with celery root and dried cucumber powder achieved improved overall liking, odor, and taste compared with the original product. This study introduces the first precursor-guided formulation strategy that enables in situ egg-like aroma generation in vegan eggs during cooking, hence providing a mechanistic basis for future flavor- and taste-focused research.