Frozen vegetables carry a reputation as the thing you settle for. That reputation is about forty years out of date. They are picked ripe and frozen within hours, while the fresh equivalent has spent a week in transport and two days on a shelf, losing exactly the things freezing preserves.
What the freezer actually does
Vegetables are blanched briefly and frozen fast, which stops the enzymes that degrade texture, colour and vitamins. The nutritional difference between frozen peas and peas that have been in a fridge for five days generally favours the frozen ones. What freezing does cost is structure. Ice crystals break cell walls, so anything you wanted to be crisp will not be. That is the whole trade, and it tells you exactly which ones to buy.
The ones worth buying
Peas, spinach, sweetcorn, broad beans, edamame, green beans and broccoli florets all freeze well because you were going to cook them soft anyway. Frozen berries are better value than fresh for anything cooked, blended or baked. Frozen fish, frozen herbs, frozen chopped onion and frozen chips are all genuinely useful and none of them is a defeat.
The ones to avoid
Anything you meant to eat raw or crisp: salad leaves, cucumber, tomatoes for a salad, celery. They come back limp because the ice has already cut through them. Whole frozen potatoes and courgette are usually disappointing too. And mixed vegetable bags tend to cook unevenly, because each vegetable in them wants a different time.
Cook them from frozen, and hot
Do not defrost first. Thawing lets the broken cells release their water and you end up steaming the vegetables in their own puddle. Straight into a hot pan with oil, in a single layer, and left alone until the water has boiled off and they start to brown. Or straight into boiling water for two minutes. Both work; the slow warm-up in a lukewarm pan is what makes them grey.
They are the reason a fridge is never empty
A bag of frozen peas, a bag of spinach and a bag of something green turn an empty fridge into a meal with rice or pasta. They cost little, keep for months and do not reproach you for not using them on Tuesday. Which makes them the most practical answer to food waste there is: vegetables that wait for you instead of the other way around.
Buy the ones you would have cooked soft anyway, cook them from frozen in a properly hot pan, and stop treating them as second best. They are frequently the better ingredient, and always the more forgiving one.