I had an early Walker too op and I think that can contribute as in they're far more interested in being on the move than sat "wasting time" eating
To be fair dd is nearly 20 and much the same now! She's definitely a "food as fuel necessary evil" type which is bewildering as her dad and I both love our food. So no idea where she's come from 
Re variety - dairy foods have most of the required nutrients in them! In theory even an adult could not only survive but even thrive on milk and some kind of small fibre portion a day alone! They're certainly a good source of protein.
and I was told to look at what she ate over the week, not daily I was told same re variety
Even adults don't eat a perfect balance every day
Honestly 1/4 banana here, a couple slices Apple there, a stick or 2 of cucumber elsewhere... all adds up eventually
My dd was eating a LOT more (both in variety and amount) than I had estimated her eating when I wasn't doing the food diary it was really quite surprising!
One day I remember I'd have thought she'd not had much fruit if not for the food diary, WITH the food diary she'd actually had 1/2 banana dnd 15 grapes over the course of the day! I actually had to pull back on the fruit a bit!
I must admit I agree with @Carrotcakey i/we ate with dd for meal times and she ate pretty much the same as us from the start of weaning, I wasn't a fan of ready made "baby foods"
She had mushy weetabix or porridge for breakfast, pasta or "deconstructed" sandwiches for lunch, I agree a constructed sandwich is a bit much for them till school age, but they can have buttered bread fingers, slices of ham or cheese, slices or sticks of cucumber, peppers etc, then whatever we were having for dinner, I never cooked with salt anyway and very strongly flavoured or spiced food it was easy to separate out a portion for her first then add the stronger flavouring for us mid way through cooking. Typically we'd have things like pasta with veg and sauce (I'd put her sauce in a wee pot on the side so she could eat the pasta with fingers if she liked and some would be dipped in the sauce and "spoon-fed") veg in baby hand sized chunks too, cottage pie spoonfed, stir fries and noodles where hers just didn't have a lot of sauce on, much mess with the noodles though
so sometimes I cheated and she had half a tortilla wrap instead, casseroles, home made soup (I'm a Scot this is practically our national dish!)
She actually really likes spicy food and strong flavours which we gradually discovered when she "stole" things off our plates! We were very surprised one time when she nabbed a VERY spicy piece of Mexican chicken off ex's plate, wolfed it down and asked for more! There was none left unfortunately. But I increased the flavouring and spice in her portions. Like me she'll happily eat garlic cloves whole and even pickled garlic.
Re banana in mouth - definitely progress! Lots of praise when he does things like that.
Do you "show" him you putting food in your mouth and doing the "mmmm yummy" thing? Demonstrating the pleasure of eating?
And yes to letting him "play" with food too, that's how they learn and get comfortable with it so don't just whip it away if he's touching, smelling, mushing it but not eating it.
My Dd did that a lot with banana at first before actually eating and enjoying, she was a bit suspicious when first presented with it.