Cut the peppers and spring onions into small fine cubes and chop the parsley. Halve the lemon, squeeze out the juice and mix with the cut vegetables in a bowl.
Prepare the rice in salted water according to the instructions on the packet.
After the rice has cooked for about 10 minutes, prepare the tuna medallions. Fry them in a little oil on both sides for 2 - 3 minutes and then let them rest briefly on a plate.
Mix the cut vegetables with the cooked rice and butter in a bowl and season with salt and pepper.
Finally, brush the tuna medallions with a little Sriracha sauce and spread the sesame seeds on top.