Prepare Zucchini: Cut both ends of the zucchini, cut in half if large, and scoop out the flesh. Reserve 150 g of the flesh.
Make the Filling: In a mixer, blend the reserved zucchini flesh and onion. In a bowl, combine this mixture with parsley, dill, oregano, minced meat, egg, salt, pepper, olive oil, vinegar, and trahana. Mix well.
Stuff Zucchini: Fill the zucchini with the mixture and place them in a saucepan.
Cook Zucchini: Add water, vegetable cube, and olive oil to the saucepan. Cover and bring to a boil, then lower the heat and cook for 35 minutes.
Prepare Egg-Lemon Sauce: In a pan, melt butter. Strain the juice from the saucepan and mix with flour in the pan. Gradually add the juice, water as needed, and cook until thickened. Off the heat, add lemon juice and egg yolks, mixing well.
Serve: Pour the egg-lemon sauce over the cooked zucchini. Serve with freshly ground pepper, chopped dill, and lemon slices.