Begin by preheating your oven to 250°F (120°C). Lower temperatures are best for these crackers because you want to toast them gently without burning the delicate seasonings or the crackers themselves.
In a medium mixing bowl, whisk together the vegetable oil, the dry Ranch dressing packet, dried dill weed, garlic powder, and lemon pepper if you are using it. Make sure the powder is well incorporated into the oil so there are no large clumps.
Place the oyster crackers in a large gallon-sized sealable plastic bag or a very large mixing bowl. Pour the seasoned oil mixture over the crackers. Seal the bag and shake gently, or toss carefully with a spatula, until every cracker is evenly coated in the ranch mixture.
Spread the coated crackers out in a single layer on a large rimmed baking sheet. Place them in the oven and bake for 20 minutes. About halfway through the baking time, give the crackers a quick stir to ensure they toast evenly on all sides.
Remove the baking sheet from the oven and let the crackers cool completely on the pan. As they cool, the coating will set and the crackers will become extra crunchy. Once cooled, they are ready to be served or stored.