I've been to Nepal from New Delhi in late 2017 and entered the coutry thru the Bhimdatta border post (the most western one) and the crossing of the river to get to Nepal is quite funny : It's an old british railway bridge that's open one way only. From there I've been riding around Dadheldura district, then off to Dhangadhi, Nepalganj, Lumbini, Tansen, Pokhara, Kathmandu and south back to India.

Everything west of Lumbini is really of the tourist beaten track. I've loved the mountain roads in Dadheldhura district (especially the one going north from the main East-West road called H01). I also loved Tansen and the road between Butwal and Pokhara.
Pokhara not so much... Too much tourists like me If you need a break from the Pokhara life, the little guest houses around Begnas lake, just a few kms east from there are awesome places to stay... I wanted to stay one night and ended up staying 5 days chilling on those hills !
If you want to go hiking on riding in some region / natural reserve, you will need a permit. I didn't get the chance to lay hand on a permit to fo riding in the Mustang and really regretted that ... But the permit is expensive and I spent all my money on the clapped out Enfield 500 we rode to get there !

I didn't get east of KTM, so I don't have any advices about that... But in case you end up in western Nepal here you go !