Work for a company in "the trades" like plumbing, electrician, insulation installation, etc. Get a license yourself after your apprenticeship. Hire people. Make a mint.
This sounds a bit more involved than "on the side" though, particularly everything leading up to licensing.
If you are hiring people to do the work, why do you need to spend time in apprenticeship?
Probably to determine quality of employee and to fully understand the process. It seems pretty risky to just assume you're not gonna screw all that part up
In California, at least, it is required. The owner is responsible for the employees' work. The employees don't have to be licensed, so the employer must be. An apprenticeship is mandatory, in California. You have to be employed by a licensed contractor for 4 years and be able to prove it (timecards, etc).