At my most neurotic, when DS was a fruit'n'veg refusenik toddler, I once found myself pureeing 3 strawberries through a tea strainer in order to hide it in yogurt or ice cream. This is NOT a tip I would recommend!
At the difficult stage rely on what you can get into smoothies, milkshakes, pasts sauces etc, and then reach for the children's vitamin supplements, which if nothing else, are good for YOUR mental health.
Then calm down and wait for them to grow up a bit.
Find things they enjoy, such as corn on the cob to eat with fingers. Include lots of veg options in a 'build your own pizza' tea. Use dips imaginatively - cooked broccoli etc can be dipped in guacomole or other veg dips. Loads of guacomole can be incuded with nachos. Avocadoes are nice mashed into sandwiches. Freeze smoothies into lollies. Actually, I freeze those Innocent fruit tube things and offer them as dessert. Have pancakes with stewed apple and yog.
DS used to enjoy eating chopped fruit with a cocktail stick - so I let him. Process is half the battle with kids. Pineapple speared on a cocktail stick, strawbs whole with the stalk on and dipped in yogurt.
For myself, I don't veg-count, but I tend to chop some fruit into meusli, or make stewed apple from the tree for breakfast, and freeze loads for the winter. We all have some fruit at breakfast - chopped pineapple, a satsuma or a kiwi in an egg cup.
Lunch - a veggie laden soup, or a sandwich of avocado and tomato and some leaves, felafels and hoummous, an innocent veg pot if they are on special offer, I keep cherry toms on my desk to pick at.
Dinner - something with a tomato based sauce plus green veg, or two veg with the main.
Some days we achieve 5, sometimes 3, sometimes loads more.