This study explores the mental lexicon of Polish learners of Spanish as a foreign language (L2) through a qualitative analysis of lexical availability. Based on prototype theory and semantic network models, it analyzes learners’ responses to two thematic prompts—‘The Human Body’ and ‘The City’—to explore lexical associations, prototypicality, and network structures. The qualitative analysis is based on the lexical production of six learners drawn at random from a larger corpus of lexical availability of B2-level students from three Polish cities. Results show a hierarchical organization around stable prototypical cores and more variable peripheral areas. Associations reflect semantic, formal, functional, and experiential links, activated by priming. The findings validate lexical availability as a tool for investigating the cognitive structure of the L2 lexicon and highlight its pedagogical value for vocabulary instruction grounded in semantic categories and associative networks.