Roughly chop some garlic cloves, sprinkle sea salt on and mix the salt into the garlic pieces, then grind it against the board with the flat of your knife - this will make a nice paste. Mix this into olive oil with lemon juice, balsamic vinegar, black pepper and chopped sprigs of rosemary, thyme & oregano (or any combo of those).
Or: veg/rapeseed oil and the garlic with lime juice, fennel seeds, cumin seeds, black pepper and chilli flakes (or chopped fresh chilli, seeds in).
By the way, chicken thighs are much, much tastier - and cheaper - than breasts, and better suited to barbecuing.