Instant controlled pressure drop (DIC) is one of the emerging technologies in food processing; it can be used for drying, freezing and the extraction of bioactive molecules without damaging their properties. Legumes, such as lentils, are one of the most consumed foods in the world; however, they are mainly cooked by boiling, which causes the loss of antioxidant compounds. This work evaluated the effect of 13 different DIC treatments (with pressure ranges of 0.1–0.7 MPa and times of 30–240 s) on the content of polyphenols (Folin–Ciocalteu and High Performance Liquid Chromatography HPLC) and flavonoids (2-aminoethyl diphenylborinate) as well as the antioxidant activity (DPPH and TEAC) of green lentils. The DIC 11 treatment (0.1 MPa, 135 s) obtained the best release of polyphenols, which in turn are related to antioxidant capacity. The abiotic stress generated by DIC could lead to the breakdown of the cell wall structure, which favors the availability of antioxidant compounds. Finally, the most efficient conditions for DIC to promote the release of phenolic compounds and maintain antioxidant capacity were found under low pressures (<0.1 MPa) and short times (<160 s).