Preheat your oven to 220°c/200 fan/425F/Gas 7
Peel and chop your sweet potato into ½ inch chunks. Toss with olive oil and a generous crack of salt & pepper.
Arrange the sweet potato chunks on a large baking sheet in a single layer and cook in the preheated oven for 30-35 minutes, tossing at the 15 minute mark, till starting to crisp around the edges. Allow to cool before adding to the rest of the salad ingredients.
To prepare the rest of the salad, first drain and rinse the tin of butter beans. Add to a large bowl with the onion, cherry tomatoes, pomegranate seeds and chopped herbs.
When the sweet potatoes are cooled, add to the bowl and mix everything together.
To make the dressing, add the oil, vinegar and lemon juice to a small jar or bowl and stir or shake to combine. Season to taste.
Drizzle the dressing over the salad, starting with 3 tablespoons. Toss together then taste and add more dressing as required. You may not need to use it all.
To cook the tuna steaks, first season them on both sides with salt & pepper then drizzle with a little olive oil.
Heat a griddle or frying pan over a high heat - you want it to be nice and hot to sear the tuna.
Add the steaks to the pan and cook over a high heat for 1-2 minutes on each side, depending on thickness. You want them to stay slightly pink in the middle.
Let the tuna rest for a couple of minutes before serving with the salad.