The aim of this work was to characterise Lenticchia di Castelluccio di Norcia (an Italian PGI lentil landrace) and assess the impact of cooking and storage on antioxidant activity. After opening the package (T0), samples were analysed using a set of chemical assays (i.e., total phenolic content, DPPH, ABTS, and ORAC assays). Analyses were also conducted on boiled, pressure-cooked, and 6-month-stored (T1) products. At both T0 and T1, raw Lenticchia di Castelluccio di Norcia PGI showed higher total phenolic content (T0: 9.08 mg GAE/g, T1: 7.76 mg GAE/g) and antioxidant activity (DPPH T0: 33.02 µmol TE/g, T1: 29.23 µmol TE/g; ABTS T0: 32.12 µmol CE/g, T1: 31.77 µmol CE/g; ORAC T0: 3.58 μmol TE/g, T1: 3.60 μmol TE/g) than boiled and pressure-cooked samples. Overall, pressure-cooking led to a smaller decline in total phenolic content and antioxidant activity than the common boiling procedure. Domestic storage led to a significant reduction in total phenolic content—both in raw and cooked products—but not in antioxidant activity. In summary, these results highlighted interesting amounts of phenols and antioxidant properties of this product, showing the impact of routine procedures. Given the relevance of pulses as sustainable plant-based meat alternatives and their importance in the prevention of non-communicable diseases, health professionals should consider these aspects in the context of correct nutrition education and scientific communication.