Before you start, preheat oven to 220°C (or 200°C fan bake). Bring a medium pot of salted tap water to a boil with the lid on.
Prep potatoes and toss on a lined oven tray with first measure of oil. Season with salt and pepper. Roast on upper oven rack for about 20 minutes, until tender. Remove from oven and crush potatoes with a masher. Drizzle with second measure of oil and roast for a further 10-12 minutes, until golden and crispy.
Prep broccoli and courgette. Pat beef dry, dice 3cm, season with salt and toss in a medium bowl with Cajun spices. Keep beef plain for fussy little foodies.
When potatoes return to oven for a second time, cook beef. Heat oil in a large fry-pan on medium-high heat. Cook beef for about 2 minutes each side for medium (depending on thickness), or until cooked to your liking. During last minute of cook time, add second measure of butter to pan and toss to coat beef. Rest, covered.
Cook broccoli and courgette in pot of boiling water for about 3 minutes, until just tender. Drain well, return to pot and toss with spinach and first measure of butter. Season to taste with salt and pepper.
Serve potatoes with beef, greens and aioli.