In a small bowl, whisk together the vegetable oil, ranch seasoning, red pepper flakes, garlic powder, and lemon pepper (if using) until fully combined with no dry clumps.
Pour the saltine crackers into a gallon-size zip-top bag or a large container, trying to keep them mostly whole.
Pour the seasoned oil evenly over the crackers, distributing it across the surface rather than in one spot.
Seal the bag most of the way, leaving a small gap for airflow, and gently turn it over several times to coat the crackers. Avoid hard shaking.
Let the crackers rest at room temperature, tossing gently every 15 minutes for the first hour, then once an hour after that, for a total rest of at least 4 hours (overnight is best).
Give the crackers one final gentle toss, then pour into a serving bowl.