Preheat the oven to 170°C (340°F). Peel and finely dice the onion, peel and thinly slice the garlic. Place the tomatoes in a bowl and crush them with your hands (or a potato masher) until you have a slightly chunky, smooth tomato sauce. Wash the lemon and grate about a quarter of the zest. Drain the beans and set aside.

Heat olive oil in a large pan and sauté the onions with a pinch of salt over medium-high heat until translucent. Once the onions are nicely translucent, add the garlic and lemon zest and sauté for another one to two minutes.

Deglaze the pan with tomato sauce. Add beans and thyme, stir well, and season with salt, pepper, and chili flakes.

If necessary, transfer the beans to a casserole dish (or leave them in the pan if it's oven-safe) and bake in a preheated oven for 35 minutes, or until the tomato sauce has thickened nicely.

After 35 minutes, remove the pan from the oven and discard the thyme. Distribute the feta over the surface and return the beans to the oven for another 10 minutes, until the feta is nice and warm. In the meantime, cut the lemon into wedges.

Serve Plaki with lemon wedges, parsley and some fresh bread or pita.