This is the "bulletproof" part. Use an Issue Tree (not a task list). You break the main question into MECE parts (Mutually Exclusive, Collectively Exhaustive).
Complex problem‑solving is the single most important 21st‑century skill; it’s teachable by following a structured cycle that forces clear problem definition, rigorous disaggregation, prioritized analysis, and persuasive synthesis.
Problem: Declining restaurant sales.