Peel the onion and halve it. Slice each half into about 6 wedges. Peel and grate or crush the garlic. Halve the cherry tomatoes.
Separate the leaves from the sprout top. Slice them into thin strips around 2 cm wide. Repeat with the remaining segments.
Heat ½ tbsp oil in a deep frying pan or wok over a medium heat. Add the onion. Fry for 5 mins till it starts to soften. Add the tomatoes. Fry for another 2-3 mins till soft.
While the tomatoes soften, fill a pan with boiling water. Bring to the boil. Add the spaghetti. Simmer for 8 mins till al dente – it should be cooked but still have a little bite to it.
Add the garlic and sliced sprout top to the frying pan. Stir well. Season with salt and pepper. Add 3 tbsp water. Cook gently for 3-4 mins till the sprout top leaves are tender.
Heat a griddle pan over a medium heat. Brush each steak on both sides with 1 tsp oil. Season with salt and pepper. Add to the hot griddle pan. Cook for 2 mins on each side till charred but still pink inside (or add on an extra 1-2 mins for well done). Pop on a plate or board to rest for a few mins.
Drain the spaghetti. Divide between two warm plates. Add the fried vegetables. Slice the steaks and arrange them on top of the veg.
Use a peeler to shave slivers off the Parmesan. Scatter over the beef. Serve straight away with
extra Parmesan on the side.