Preheat the oven to 450F or 425F convection. Line a baking sheet with parchment paper (see note). Add the leeks, carrots, and fennel to the baking sheet and toss with the oil, ½ teaspoon salt, and pepper.
In a medium bowl, whisk the egg. Add the lamb, almond flour, mint, garlic, salt, and pepper and use your hands to mix thoroughly, trying not to overmix. Form in about 16 golf ball-sized balls. Nestle the meatballs onto the baking sheet. Brush the tops of the meatballs with some olive oil (this isn’t totally necessary, but helps them get nice and brown on top).
Bake for 12-15 minutes, then transfer to the top rack and broil for about 3-5 more minutes (keeping an eye on it), or until the meatballs are browned on top and veggies are browning/charring a bit.
In a small bowl, mix together the yogurt, lemon, garlic (if you want a more garlicky yogurt) and remaining ½ teaspoon salt. Plop some of the yogurt (about ¼ cup) onto your plate and use a spoon to smear it. Top with veggies, meatballs, herbs, black pepper, and a squeeze of lemon.