You can get tins of pretty much any bean, less so for lentils because the smaller ones cook down to a mush!
That being said, most lentils such as red, green , puy, cook from dry in about 30-40 mins, so aren't any effort really to throw in to whatever you're cooking.
My fave ways to 'bulk up' stuff to add fibre and texture (and save money!) are:
Kidney beans in chilli/shephards pie
Butter beans or cannellini beans in spagbol/hm burgers/macaroni cheese (trust me!)/pasta bakes
red lentils in soups that lend themselves to the bright colour
Green lentils or brown lentils in stews and casseroles
Chickpeas in stirfries, soups and stews (esp morrocan type one!)
And as far as I've found, you can add most types of pulse to a curry and it tastes lovely, my fave being chickpeas and split peas!
If you soak beans over night (or at least 6 hrs) then they often still need around 1hr cooking in boiling water. Not hard but make sure to plan ahead!
You can't put stuff like kidney beans straight in to a stew or slow cooker without first boiling for at least 10 mins to get rid of a toxin.
The cans are still really cheap so deffo stock up on those too for when you need them last minute. Also I've been trying to cook a whole bag of dried all at once and freeze in a ziplock bag to just use as and when. It works really well!!