'Vegetables at every meal' is good general guidance and bad rigid prescription. Total daily vegetable intake matters more than per-meal balance. A plate of pasta now and a big salad later in the day works similarly to having salad with the pasta.
What the actual evidence supports
5+ servings of fruit and vegetables daily for general health benefit. 30+ different plant foods weekly for microbiome diversity (stronger evidence than the '5 a day' framing). Both achievable with varied eating across the day rather than rigid per-meal structure.
Where the per-meal framing helps
Building habit: 'vegetable at every meal' is simpler to remember than 'total daily intake'. Calorie management: vegetables add volume and reduce intake of higher-calorie foods. Nutritional density: spreading vegetables across day distributes nutrients.
Don't stress if some meals don't have vegetables. Aim for daily totals. The flexible approach is more sustainable than the rigid one for most people.