Wash the chicken breast fillets under cold water and pat dry with kitchen paper.
Peel the onion and cut into thin slices. Divide the slices into rings. Peel the garlic and finely chop or press. Wash oregano, pat dry and roughly chop. If you like, you can also add a little fresh rosemary, but only a little, because otherwise it tastes too strong. Mix all marinade ingredients together.
Parry the chicken breast fillets and make 2-3 incisions in the thick part. Marinate fillets overnight, preferably in a freezer bag.
Grill on the charcoal grill for a total of 5-6 minutes.
As a side dish is e.g., Rice and spinach pot (such as the one from CK user Crazy_Melly).