Hello ruby -
My DH invented a fabulous recipe with tuna. Probably not easy to cook for more than say 4 people but it's really delicious.
Marinade tuna steaks in some soy sauce, sesame oil (proportions like a salad dressing I guess - about 3 soy to 1 sesame). Add in some chopped ginger, chilli and garlic and maybe a squeeze of lime juice. I think it's about 4 cloves, 4 tsp of that ready chopped ginger and 2 tsp of ready chopped chilli for 4 people.
Marinade for as long as you have - at least 20-30 mins but can sit for hours if you want. Pan fry or griddle - time depends on how raw you want it (I have to have it cooked through at mo as I'm pg, but it's delicious slightly rare inside).
We serve it with some simple stirfried veggies (e.g. carrots, peppers, broccoli, cherry toms) done in oyster sauce, and rice. you can make the rice look posh and dinner party-esque just by piling it into a teacup or glass and turning it out on to the plate in a big tower!
It's a bit last minute, as you have to do the veggies and tuna just before serving, but it is very quick at that stage. Rice can usually sit in a pan keeping warm for a while so you don't have to faff with that as well.