With the growing demand for healthy and sustainable foods, it is likely that we will see an increase in the use of alternative ingredients that are rich in dietary fiber and antioxidants. In this context, unconventional flours such as mixed unripe banana pulp and peel flours emerge as potential food ingredients. Besides their technological properties, these flours are notable for their functional compounds, especially resistant starch, other dietary fibers, and phenolic compounds. This study aimed to evaluate the effect of adding mixed green banana pulp and peel flours in the ratio of 90:10 (M1) and 80:20 (M2) (pulp:peel flours), on the resistant starch concentration of lemon zest biscuits. Four different formulations were developed—FC (control, 100% corn starch), F100PF (50% green banana pulp flour), FM1 (50% of M1), and FM2 (50% of M2). The biscuits were evaluated for technological parameters (e.g., water activity, color, and firmness) and resistant starch content. The F100PF, FM1, and FM2 formulations showed a significant increase in hardness, ranging from 5.79 N (F100PF) to 9.81 N (FM2). Additionally, the addition of the unripe banana flour in the F100PF, FM1, and FM2 formulations significantly reduced the luminosity parameters (L*), and increases the water activity in the FM1 (0.60) formulation. It was also observed that the resistant starch content was nearly five times higher in F100PF (5.86%), FM1 (5.72%), and FM2 (4.25%) compared to the control formulation (0.98%). These results suggest that mixed green banana flour can be an excellent alternative for producing biscuits that are rich in dietary fiber, contributing to a more balanced and functional diet.