Heat the oil in a pan and cook the onions for 5-10 minutes until soft, adding the garlic for the last minute. Stir in the mushrooms and cook for a further 5 minutes until golden brown. Drain the salmon and stir in. Heat through for 1 minute.
Meanwhile, cook the pasta according to the instructions on the packet. Cook the broccoli in a pan of boiling water for 3 minutes, then drain. When cooled a little, roughly slice.
Drain the pasta and stir through the salmon sauce and broccoli. Serve immediately.