HEAT an extra-large non-stick frying pan over medium-high. Add 1 tbsp olive oil, then onion. Cook until onion is soft and brown, 5 to 7 min.
STIR in garlic, 1/2 tsp salt and cabbage. Season with fresh pepper. Cook, stirring often, until cabbage begins to soften, 3 to 5 min. Pour in vegetable broth. Reduce heat to medium-low. Simmer, stirring occasionally, until most of the liquid has evaporated, 5 to 7 min. Transfer cabbage to a platter.
PAT dry salmon fillets. Sprinkle remaining 1/4 tsp salt over both sides. Season with fresh pepper.
WIPE pan clean, then return to stovetop over medium-high. Add remaining 1 tbsp olive oil, then salmon, skin-side down. Cook for 2 min. Reduce heat to medium and continue cooking until bottom is golden, about 4 min. Flip fillets and cook for 1 min more or until a knife tip inserted in centre of fish and held for 10 sec comes out warm. Serve, skin-side down, over cabbage. Sprinkle with green onion.