Rethink your training split! If you aren’t even considering a full body, upper/lower, or push/pull/legs split you could be missing out on some gains. If the one day a week plan(chest on Monday) works for you then by all means keep at it. But if a body part is lagging I would recommend an additional 2 or 3 days a week. I personally enjoy push/pull/legs. Give it a try!