MetED has a lot of courses that you can take, depending on how in-depth you want to go. I'm taking several myself. If you just have 'basic' training, see if your NWS office offers Advanced training (essentially Meteorology 101 for spotters), again, depending on how in-depth you want to go.
NWS Paducah, KY offers Elite training, which is essentially the 'Meteorology 101' from Advanced training if you get it, but also places emphasis on mobile spotter safety and basic radar fundamentals; they also offer 'mini courses' on topics like radar fundamentals (going more in-depth on topics lightly covered in Elite training) and extreme tornado risks.