When you say running for 40/45 minutes per week, do you mean 1x40 minute run a week or is that split up over a few days or say 3x40 minute runs? What kind of intensity are they for? And how are you feeling at the end of runs?
Garmin have a decent range of Training Plans which might be worth following, they start off with a fitness test and then can customise based on where you're at and how often you can run a week. You'd probably get more out of something like that than a generic plan online, as from memory you have a decent level of fitness from prior stuff so less need to take it as slow initially.
If you didn't want a plan, then assuming you're doing 3-4 runs a week, i'd probably try and structure it a little like the following, although i'm by no means an expert
Run 1 - Easy 40 min run
Run 2 - Easy 30 min run and finish with some strides (15 second fast (but not all out sprint) events with a 45second walk recovery)
Run 3 - Easy 40 min run
Run 4 - Easy 60 minute run, split up into 15 mins running, 5 mins fast walking x3. Then in later weeks increase the run and reduce the walk
That would kind of tick off most of what you'd want to aim for as far as variety goes. The theory would be that the progression would then be to either add in another session or turn some of the 40 min runs into a 60 minute run eventually and the long run increases too.
