Peel onions and garlic. Finely dice the light onion. Cut red onion into rings. Finely dice garlic. Sort and wash the rocket and chop finely, except for something to garnish. Drain the tuna.
Mix half the cheese, rocket and garlic, season with salt and pepper. Mix the remaining cheese, tuna and diced onion, season with salt and pepper.
Cut the bread into slices about 1 cm thick, spread a thin layer of oil on both sides and fry them crisply in portions on both sides in a hot pan. Cut off 8 dumplings from both creams with 2 tablespoons of each and place each on a slice of bread.
Garnish with rocket and onion rings. Add remaining slices of bread and creams.