A vegetarian dish can be well seasoned and still feel incomplete. The missing element is frequently structural, since meat provides a resistance that most plant ingredients do not.
Meat's texture comes from aligned fibres
Muscle is built from long fibres bundled in connective tissue, and biting across those bundles produces a resistance that then gives way.
Cooking changes this predictably, with proteins tightening and connective tissue converting to gelatine over longer cooking.
Plant foods have no equivalent structure, since their cells are individually walled and roughly isotropic, so they yield uniformly instead of shearing.
Uniform softness reads as unfinished
A dish where everything has the same texture gives the mouth no information to work with, and it registers as monotonous regardless of how it tastes.
Many vegetarian dishes drift this way because vegetables cooked in one pot converge towards a similar softness.
Which is why adding contrast, rather than adding flavour, is usually the correction for a dish that seems adequate but unsatisfying.
Contrast can be built at several points
Texture is easiest to introduce at the end, where nothing further will soften it, which is why toasted nuts, seeds, fried aromatics and raw elements are so effective.
It can also be built during cooking, by roasting part of a vegetable while boiling the rest, or by holding back a portion to add late.
Legumes cooked to different degrees within the same dish achieve this too, with some breaking down to thicken and others staying intact.
Some plant ingredients do provide structure
Certain preparations have fibrous or layered structures of their own, including some fungi, wheat gluten preparations, and pressed or frozen bean curd.
Freezing bean curd changes its structure by forming ice crystals that leave a spongier network behind after thawing, which then holds sauce differently.
These are worth understanding on their own terms rather than as imitations, since their behaviour under heat differs from meat in useful ways.
Fat contributes to the sensation of substance
Part of what makes a dish feel substantial is the coating that fat leaves in the mouth, which lingers after swallowing.
Lean vegetable dishes often lack this, and adding a suitable fat late frequently resolves a dish that seemed thin despite adequate seasoning.
The choice of fat matters, since one with its own flavour contributes on both counts while a neutral one addresses only the texture.