• Wash and trim the stems off of the zucchini. Peel most of the skin off allowing a few strips to remain. Bring a large pot of water to boil and add the zucchini whole to the pot. Boil the zucchini for 5 – 10 minutes until tender but not mushy. This will make it easier to hollow out the centers and cut down on cooking time.

Prepare the meat filling:

• In a large skillet or sauce pan, heat 1/4 cup olive oil over medium high heat. Add the onion and sauté until translucent, about 5 -7 minutes. Add the garlic and sauté until fragrant, about a minute.
• Add the ground beef and saute until the meat is no longer pink. Add the parsley, mint, tomatoes, and season lightly with salt and freshly ground black pepper.
• Cook the meat sauce uncovered until most of the liquid evaporates. Stir in 1/2 cup grated Kefalotyri cheese and set aside.
• Carefully drain the zucchini. Slice them in half (lengthwise) and hollow out the centers of the zucchini. Be careful not to puncture the skin. Try to leave about a 1/4 inch thickness of flesh to give the zucchini boats support.
• Preheat the oven to 375 degrees.
• Place the zucchini boats on a lightly greased sheet pan. Fill each with the ground meat filling, pressing lightly to even the surface.

Prepare the béchamel sauce:

• Melt butter in a saucepan over low heat. Using a whisk, add flour to melted butter whisking continuously to make a smooth paste or roux. Allow the flour/butter mixture to cook for a minute but do not allow it to brown.
• Add warmed milk to mixture in a steady stream, whisking continuously. Simmer over low heat until it thickens but does not boil.
• Remove from heat and stir in beaten egg yolk. Add pinch of nutmeg. If sauce still needs to thicken, return to heat and cook over very low heat while continuing to stir.
• Bechamel is thicker than gravy but not quite as thick as pudding. It should be somewhere in between. One way to tell if it is thick enough is to dip your wooden spoon in the sauce and draw your finger across the back of the spoon. If the sauce holds a visible line then it is thick enough.
• Spoon the béchamel sauce over the meat filling in each half and sprinkle tops with remaining 1/2 cup grated cheese. If you wish, you can save any extra béchamel for serving. Bake in a preheated 375 degree oven until the zucchini is cooked through and the béchamel sauce is golden brown (about 30 minutes).
• If your béchamel doesn’t brown, you can switch the heat setting to broil in the last few minutes of cooking making sure not to scorch the tops.