Slice the onions and put into a pan on a very low heat with a small knob of butter and a drop of oil.
Let the onions cook down for about 15 minutes. During this time, drain the capers and marinate them in olive oil and a little seasoning.
Lightly smash potatoes with butter, salt, and pepper. Place in a ring, with rocket on top.
Add three to four slices of tomato on top, then the cooked down red onion on top of that, then the capers, then the goats' cheese.
Place under medium grill for two to three minutes.
Serve with retained rocket and olive oil.