Don't feel bad op, no parent is perfect and it's definitely better to be giving him fruit than chocolate!
I allow my two (4.5 and almost 2) to eat as much as they like at mealtimes, they can have seconds and then I offer fruit and Greek yoghurt, after that sometimes DS will ask for an apple too. But we rarely have snacks, DS would sometimes ask for an apple in the middle of the afternoon and I give him that as I don't want to restrict food but don't want to actively encourage snacking.
As another poster said, snacks are things that we have for pleasure when we're out somewhere. DS will sometimes ask for chocolate when we're in the shop or paying for petrol (especially ATM as he's become used to having chocolate over Easter - shows what a slippery slope it can be!) but I tell him no and deal with moaning, and if he asks for some and I do have some in the house I tell him he can have it after dinner as we need to make sure we eat the food that helps out brain and body grow first.
My pair eat almost the same at the moment as DD must be having a crazy growth spurt, so a normal day for them would be:
Breakfast: porridge / weetabix with full fat milk and half a banana mashed in
Lunch: sandwich with two slices of wholemeal bread - always protein based, so usually egg mayo, tuna or chicken. I also mash in an avocado sometimes to reduce the amount of Mayo and up the protein. Or if they're at home it's beans on toast or French toast or scrambled egg & smoked salmon with toast. Then berries/pineapple/grapes/mango with Greek yoghurt.
Dinner: mostly always protein, like spaghetti Bol - I do think we eat too much pasta but it's something they love and eat. They love brocolli and peas so if we aren't having a tomato based dinner that I can pack veg into, I'll throw some brocolli or peas into the dinner.
I used to be veggie and have a preference for non animal protein - Greek yoghurt is great, as are baked beans, eggs, cheese and avocado.
Vegetable wise.... DS isn't a great lover of veg but I learnt my lesson with DD and have encouraged stuff like olives, pickles, gherkins etc which she seems to love ( though she may just be a strange girl!!) but stuff like that could be good to try.