Place all the ingredients for the meatballs in a medium mixing bowl. Mix with your hands until the ingredients are well combined. Refrigerate for 20 minutes to let the chia seeds work their gelling magic.
Meanwhile, pre-heat the oven to 375 degrees. Line a rimmed baking sheet with foil. Spray a rack with cooking spray and place it on top of the baking sheet.
Gently roll the meat mixture into 18 balls, roughly 2-inches in diameter, and place the balls on the prepared rack. Bake for 22-23 minutes until lightly brown and cooked through. (Or until the balls register an internal temperature of 160 degrees.)
While those balls are baking, get going on the yogurt sauce. In a small bowl, whisk together the tahini and warm water until smooth. Transfer the tahini mixture to the bowl of a food processor and add the yogurt, basil leaves, garlic, lemon juice, and a good pinch of kosher salt. Process until smooth, scraping down the sides of the bowl a few times if necessary. (Yes, you can do this in a blender if you don’t have a food processor.)
Serve the meatballs warm with plenty of yogurt sauce.