I think its a good idea to try and fit veggies into at least 3 meals of your day and just eat the suggested serving size. Like one banana is approx 29 carbs, 85grams of spinach is 10 carbs etc.
As for how much you should eat during one sitting you divide the number of calories etc by the number of meals you eat in the day and use those number as baselines for each meal.
Some recommend to taper your meals having your breakfast as your largest meal and your supper the smallest. So say you eat 3500 cal's a day with 6 meals you would eat say 666 cals for breafast then 583 for meals 2-5 then 500 for meal 6.
Use the macro's depending on your diet to figure out carbs, protein, fat