Add the yogurt to a muslin cloth or to a colander set over a bowl. Hang for at least an hour, or up to 4 hours. This can be done up to a day in advance and the labneh can be kept refrigerated.
Heat the butter and olive oil in a pot and add the onions. Season with salt and pepper. Cook over a medium heat until the onions brown around the edges and caramelize. If they start to brown too quickly, turn the heat down and cover and cook for a few mins.
Cook the peas in boiling salted water for a few mins until tender. Drain and set aside.
Make the chilli butter: heat the oil and butter in a small pan and add the garlic cloves and chilli powder. Swirl the pan above the flame for no more than 20 seconds. Set aside.
Add the labneh to a bowl and stir in the minced garlic, caramelized onions, lettuce and peas. Taste and adjust seasoning. Top with chopped parsley and pour over the chilli butter. Best eaten as a dip with garlic bread.